Phytoestrogens and mycotoxins in Iowa streams: an examination of underinvestigated compounds in agricultural basins

This study provides the first broad-scale investigation on the spatial and temporal occurrence of phytoestrogens and mycotoxins in streams in the United States. Fifteen stream sites across Iowa were sampled five times throughout the 2008 growing season to capture a range of climatic and crop-growth conditions. Basin size upstream from sampling sites ranged from 7 km2 to > 836,000 km2. Atrazine (herbicide) also was measured in all samples as a frame-of-reference agriculturally derived contaminant. Target compounds were frequently detected in stream samples: atrazine (100%), formononetin (80%), equol (45%), deoxynivalenol (43%), daidzein (32%), biochanin A (23%), zearalenone (13%), and genistein (11%). The nearly ubiquitous detection of formononetin (isoflavone) suggests a widespread agricultural source, as one would expect with the intense row crop and livestock production present across Iowa. Conversely, the less spatially widespread detections of deoxynivalenol (mycotoxin) suggest a more variable source due to the required combination of proper host and proper temperature and moisture conditions necessary to promote Fusarium spp. infections. Although atrazine concentrations commonly exceeded 100 ng L(-1) (42/75 measurements), only deoxynivalenol (6/56 measurements) had concentrations that occasionally exceeded this level. Temporal patterns in concentrations varied substantially between atrazine, formononetin, and deoxynivalenol, as one would expect for contaminants with different source inputs and processes of formation and degradation. The greatest phytoestrogen and mycotoxin concentrations were observed during spring snowmelt conditions. Phytoestrogens and mycotoxins were detected at all sampling sites regardless of basin size. The ecotoxicological effects from long-term, low-level exposures to phytoestrogens and mycotoxins or complex chemicals mixtures including these compounds that commonly rake place in surface water are poorly understood and have yet to be systematically investigated in environmental studies.     

Effect of Climate Warming and Drought on Urban Stream Temperatures in a Semiarid,Seasonal System

Stream temperatures are key indicators for aquatic ecosystem health, and are of particular concern in highly seasonal, water‐limited regions such as California that provide sensitive habitat for cold‐water species. Yet in many of these critical regions, the combined impacts of a warmer climate and urbanization on stream temperatures have not been systematically studied. We examined recent changes in air temperature and precipitation, including during the recent extreme drought, and compared the stream temperature responses of urban and nonurban streams under four climatic conditions and the 2008–2018 period. Metrics included changes in the magnitude and timing of stream temperatures, and the frequency of exceedance of ecologically relevant thresholds. Our results showed that minimum and average daily air temperatures in the region have increased by >1°C over the past 20 years, warming both urban and nonurban streams. Stream temperatures under drought warmed most (1°C–2°C) in late spring and early fall, effectively lengthening the summer warm season. The frequency of occurrence of periods of elevated stream temperatures was greater during warm climate conditions for both urban and nonurban streams, but urban streams experienced extreme conditions 1.5–2 times as often as nonurban streams. Our findings underscore that systematically monitoring and managing urban stream temperatures under climate change and drought is critically needed for seasonal, water‐limited urban systems.     

PESTICIDES IN GROUND WATER: DO ATRAZINE METABOLITES MATTER?1

ABSTRACT: Atrazine and atrazine-residue (atrazine + two metabolites - deethylatrazine and deisopropylatrazine) concentrations were examined to determine if consideration of these atrazine metabolites substantially adds to our understanding of the distribution of this pesticide in groundwater of the midcontinental United States. The mean of atrazine.residue concentrations was 53 percent greater than that of atrazine alone for those observations above the detection limit (> 0.05 μg/l). Furthermore, a censored regression analysis using atrazine-residue concentrations revealed significant factors not identified when only atrazine concentrations were used. Thus, knowledge of concentrations of these atrazine metabolites is required to obtain a true estimation of risk of using these aquifers as sources for drinking water, and such knowledge also provides information that ultimately may be important for future management policies designed to reduce atrazine concentrations in ground water.     

OCCURRENCE OF TOTAL DISSOLVED PHOSPHORUS IN UNCONSOLIDATED AQUIFERS AND AQUITARDS IN IOWA1

ABSTRACT: Seven sets of ground water samples from 103 observation wells were analyzed for total dissolved phosphorus (TDP) in four areas and five materials including loess and loess derived alluvium in the Deep Loess Hills of western Iowa, outwash and fractured till adjacent to Clear Lake in north central Iowa, fractured till in central Iowa, and a sand and gravel aquifer in northwest Iowa. Land use in ground water recharge zones in all four areas is dominated by crop or animal production or both. Concentrations of TDP exceeding the minimum laboratory detection limit of 20 μg/l as P were found in all areas and in all materials sampled. Samples from the outwash deposits associated with Clear Lake contained significantly larger concentrations than all other areas and materials with a median of 160 μg/l. Water from fractured till in three areas produced the smallest range of concentrations with a median of 40 μg/l. The mean value of TDP in all sample sets exceeded 50 μg/l, an important ecological threshold that causes increased productivity in lakes and perennial streams and one being considered as a surface water nutrient standard by regulatory agencies. These results clearly show that ground water in essentially all near‐surface aquifers and aquitards discharging to Iowa's streams and lakes is capable of sustaining P concentrations of 50 to 100 μg/l in streams, lakes, and reservoirs. Consequently, even if point discharges and sediment sources of P are substantially reduced, ground‐water discharge to surface water may exceed critical thresholds under most conditions.     

Comparative losses of glyphosate and selected residual herbicides in surface runoff from conservation-tilled watersheds planted with corn or soybean

Residual herbicides regularly used in conjunction with conservation tillage to produce corn ( L.) and soybean [ (L.) Merr] are often detected in surface water at concentrations that exceed their U.S. maximum contaminant levels (MCL) and ecological standards. These risks might be reduced by planting glyphosate-tolerant varieties of these crops and totally or partially replacing the residual herbicides alachlor, atrazine, linuron, and metribuzin with glyphosate, a contact herbicide that has a short half-life and is strongly sorbed to soil. Therefore, we applied both herbicide types at typical rates and times to two chisel-plowed and two no-till watersheds in a 2-yr corn/soybean rotation and at half rates to three disked watersheds in a 3-yr corn/soybean/wheat-red clover ( L.- L.) rotation and monitored herbicide losses in surface runoff for three crop years. Average dissolved glyphosate loss for all tillage practices, as a percentage of the amount applied, was significantly less ( ≤ 0.05) than the losses of atrazine (21.4x), alachlor (3.5x), and linuron (8.7x) in corn-crop years. Annual, flow-weighted, concentration of atrazine was as high as 41.3 μg L, much greater than its 3 μg L MCL. Likewise, annual, flow-weighted alachlor concentration (MCL = 2 μg L) was as high as 11.2 and 4.9 μg L in corn- and soybean-crop years, respectively. In only one runoff event during the 18 watershed-years it was applied did glyphosate concentration exceed its 700 μg L MCL and the highest, annual, flow-weighted concentration was 3.9 μg L. Planting glyphosate-tolerant corn and soybean and using glyphosate in lieu of some residual herbicides should reduce the impact of the production of these crops on surface water quality.     

Prediction of the Fate and Transport Processes of Atrazine in a Reservoir

The fate and transport processes of a toxic chemical such as atrazine, an herbicide, in a reservoir are significantly influenced by hydrodynamic regimes of the reservoir. The two-dimensional (2D) laterally-integrated hydrodynamics and mass transport model, CE-QUAL-W2, was enhanced by incorporating a submodel for toxic contaminants and applied to Saylorville Reservoir, Iowa. The submodel describes the physical, chemical, and biological processes and predicts unsteady vertical and longitudinal distributions of a toxic chemical. The simulation results from the enhanced 2D reservoir model were validated by measured temperatures and atrazine concentrations in the reservoir. Although a strong thermal stratification was not identified from both observed and predicted water temperatures, the spatial variation of atrazine concentrations was largely affected by seasonal flow circulation patterns in the reservoir. In particular, the results showed the effect of flow circulation on spatial distribution of atrazine during summer months as the river flow formed an underflow within the reservoir and resulted in greater concentrations near the surface of the reservoir. Atrazine concentrations in the reservoir peaked around the end of May and early June. A good agreement between predicted and observed times and magnitudes of peak concentrations was obtained. The use of time-variable decay rates of atrazine led to more accurate prediction of atrazine concentrations, while the use of a constant half-life (60 days) over the entire period resulted in a 40% overestimation of peak concentrations. The results provide a better understanding of the fate and transport of atrazine in the reservoir and information useful in the development of reservoir operation strategies with respect to timing, amount, and depth of withdrawal.     

HERBICIDE CONTAMINATION BY THE 1993 GREAT FLOOD ALONG THE MISSISSIPPI RWER1

ABSTRACT: The Great Flood of 1993 inundated more than 355,000 ha of illinois cropland, creating great concern for the possible contamination of farmland by herbicides. The objective of this study was to assess the herbicide contamination of floodwaters and farmland due to the great flood of 1993. Floodwater samples were collected between August 5 and December 20, 1993, at the Horseshoe Lake State Game Reserve in Alexander County, Illinois, USA. Water and suspended sediment were tested separately for the more commonly used herbicides in Illinois and the midwestern USA: alachior, atrazine, and cyanazine. These herbicides were detected in the floodwater samples, but concentrations were all below the health advisory concentration of 3 μg/L established for drinking water by the United States Environmental Protection Agency. No herbicides were detected in the suspended sediment. After the recession of the flood, soil samples from flooded and non-flooded corn fields were collected for comparison. Soil samples taken from two out of three sampling locations had a 0.4 to 0.8 μg/kg increase in atrazine at the flooded verses the non-flooded sites. Concentrations were 500 to 1,000 times lower than the recommended 1 mg/kg rate at which this herbicides typically applied to soil.     

EFFECTS OF URBANIZATION ON CHANNEL INSTABILITY1

ABSTRACT: Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process‐based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk‐based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed‐specific conditions. In addition to the storage characteristics of the pre‐development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk‐based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.     

Stream and Retention Pond Thermal Response to Heated Summer Runoff From Urban Impervious Surfaces1

Abstract: Runoff from parking lots during summer storms injects surges of hot water into receiving water bodies. We present temperature data collected near urban storm sewer outfalls in Blacksburg, Virginia, using arrays of sensors in a stream and a stormwater pond. Surges occurred roughly a dozen times per month, ranging up to 8.1°C with average duration 2 h in the stream and up to 11.2°C with average duration 7 h in the pond. Surges were larger in the pond due to a larger contributing watershed, no dilution by upstream water, and cool background temperatures near the outfall. Surges began abruptly, warming at rates averaging 0.2°C/min for periods of 5‐20 min. Surges dissipated as they propagated into the water bodies, travelling further in the stream (>19 m) than the pond (～10 m) consistent with greater advection in the stream. Surges were largest and most frequent in the afternoon but occurred at all times of day and night. Stream surges exhibited two phases: an early high‐temperature low‐volume input from the storm sewer and a later low‐temperature high‐volume input from upstream. Surges at the pond did not exhibit two phases, consistent with inputs only from storm sewers. Surges are likely common in urban areas, and may cumulatively have consequences for aquatic organisms, biogeochemical process rates, and even human health. Such effects may be compounded by urban heat islands and climate change, so prevention or mitigation should be considered.     

Spatial and Temporal Patterns of Endocrine Active Chemicals in Small Streams Indicate Differential Exposure to Aquatic Organisms

Alkylphenolic chemicals (APCs) and hormones were measured six times from February through October 2007 in three Minnesota streams receiving wastewater to identify spatial and temporal patterns in concentrations and in estrogen equivalency. Fish were collected once during the study to evaluate endpoints indicative of endocrine disruption. The most commonly detected APCs were 4‐tert‐octylphenol and 4‐nonylphenol and the most commonly detected hormones were estrone and androstenedione. Chemical concentrations were greatest for nonylphenol ethoxycarboxylates (NPECs) (5,000‐140,000 ng/l), followed by 4‐nonlylphenol and 4‐nonylphenolethoxylates (50‐880 ng/l), 4‐tert‐octylphenol and 4‐tert‐octylphenolethoxylates with concentrations as great as 130 ng/l, and hormones (0.1‐54 ng/l). Patterns in chemicals and estrogen equivalency indicated that wastewater effluent is a pathway of APCs and hormones to downstream locations in this study. However, upstream contributions can be equally or more important indicating alternative sources. This study indicates that aquatic organisms experience both spatially and temporally variable exposures in the number of compounds, total concentrations, and estrogenicity. This variability was evident in fish collected from the three rivers as no clear upstream to downstream pattern of endocrine disruption endpoints emerged.     

Dealing With Uncertainty When Assessing Fish Passage Through Culvert Road Crossings

Assessing the passage of aquatic organisms through culvert road crossings has become increasingly common in efforts to restore stream habitat. Several federal and state agencies and local stakeholders have adopted assessment approaches based on literature-derived criteria for culvert impassability. However, criteria differ and are typically specific to larger-bodied fishes. In an analysis to prioritize culverts for remediation to benefit imperiled, small-bodied fishes in the Upper Coosa River system in the southeastern United States, we assessed the sensitivity of prioritization to the use of differing but plausible criteria for culvert impassability. Using measurements at 256 road crossings, we assessed culvert impassability using four alternative criteria sets represented in Bayesian belief networks. Two criteria sets scored culverts as either passable or impassable based on alternative thresholds of culvert characteristics (outlet elevation, baseflow water velocity). Two additional criteria sets incorporated uncertainty concerning ability of small-bodied fishes to pass through culverts and estimated a probability of culvert impassability. To prioritize culverts for remediation, we combined estimated culvert impassability with culvert position in the stream network relative to other barriers to compute prospective gain in connected stream habitat for the target fish species. Although four culverts ranked highly for remediation regardless of which criteria were used to assess impassability, other culverts differed widely in priority depending on criteria. Our results emphasize the value of explicitly incorporating uncertainty into criteria underlying remediation decisions. Comparing outcomes among alternative, plausible criteria may also help to identify research most needed to narrow management uncertainty.     

MODELING TO EVALUATE MACROPHYTE INDUCED IMPACTS TO DISSOLVED OXYGEN IN A TAILWATER RESERVOIR1

ABSTRACT: Effects of aquatic macrophytes are not considered in most standard water quality models. This study used field measurements and water quality models to help determine the effects of aquatic macrophytes on dissolved oxygen (DO) concentrations in a shallow tailwater reservoir. Installation of a hydropower plant and macrophytes (primarily Potamogeton and Chara) in a large shallow portion of the lake are possible causes of reduced DO levels in the tailwater reservoir. A water quality model (WASP5) was used to quantify the various DO sources and sinks and to evaluate the effects of the hydropower operations on DO levels in the lake. It was found that the macrophytes in Lake Ogallala had a significant effect on the DO levels in the lake. At an average macrophyte density of about 6,360 g/m² (wet weight) in 2000, the DO fluctuated daily from about 3 mg/l to about 12 mg/l. At an average macrophyte density of about 2,120 g/m² (wet weight) in 2002, the DO fluctuated from about 5 mg/l to about 9 mg/l daily. The model predicted that the DO would remain near 5 mg/l without macrophytes. The photo‐synthetic and respiration rates developed in the model (4.4 mg/g‐hr and 1.4 mg/g‐hr, respectively) agree well with literature values.     

Streamflow Responses to Climate Change: Analysis of Hydrologic Indicators in a New York City Water Supply Watershed

Recent works have indicated that climate change in the northeastern United States is already being observed in the form of shorter winters, higher annual average air temperature, and more frequent extreme heat and precipitation events. These changes could have profound effects on aquatic ecosystems, and the implications of such changes are less understood. The objective of this study was to examine how future changes in precipitation and temperature translate into changes in streamflow using a physically based semidistributed model, and subsequently how changes in streamflow could potentially impact stream ecology. Streamflow parameters were examined in a New York City water supply watershed for changes from model‐simulated baseline conditions to future climate scenarios (2081‐2100) for ecologically relevant factors of streamflow using the Indicators of Hydrologic Alterations tool. Results indicate that earlier snowmelt and reduced snowpack advance the timing and increase the magnitude of discharge in the winter and early spring (November‐March) and greatly decrease monthly streamflow later in the spring in April. Both the rise and fall rates of the hydrograph will increase resulting in increased flashiness and flow reversals primarily due to increased pulses during winter seasons. These shifts in timing of peak flows, changes in seasonal flow regimes, and changes in the magnitudes of low flow can all influence aquatic organisms and have the potential to impact stream ecology.     

INFILTRATION OF ATRAZINE AND METABOLITES FROM A STREAM TO AN ALLUVIAL AQUIFER1

ABSTRACT: The infiltration of atrazine, deethylatrazine, and deisopropylatrazine from Walnut Creek, a tributary stream, to the alluvial valley aquifer along the South Skunk River in central Iowa occurred where the stream transects the river's flood plain. A preliminary estimate indicated that the infiltration was significant and warrants further investigation. Infiltration was estimated by measuring the loss of stream discharge in Walnut Creek and the concentrations of atrazine and its metabolites deethylatrazine and deisopropylatrazine, in ground water 1 m beneath the streambed. Infiltration was estimated before application of agrichemicals to the fields during a dry period on April 7, 1994, and after application of agrichemicals during a period of small runoff on June 8, 1994. On April 7, the flux of atrazine, deethylatrazine, and deisopropylatrazine from Walnut Creek into the alluvial valley aquifer ranged from less than 10 to 60 (μg/d)/m², whereas on June 8 an increased flux ranged from 270 to 3060 (μg/d)/m². By way of comparison, the calculated fluxes of atrazine beneath Walnut Creek, for these two dates, were two to five orders of magnitude greater than an estimated flux of atrazine to ground water caused by leaching from a field on a per-unit-area basis. Furthermore, the unit-area flux rates of water from Walnut Creek to the alluvial valley aquifer were about three orders of magnitude greater than estimated recharge to the alluvial aquifer from precipitation. The large flux of chemicals from Walnut Creek to the alluvial valley aquifer was due in part to the conductive streambed and rather fast ground water velocities; average vertical hydraulic conductivity through the streambed was calculated as 35 and 90 m/d for the two sampling dates, and estimated ground water velocities ranged from 1 to 5 m/d.     

Statewide Survey of Hormones and Antibiotics in Surface Waters of Delaware

Water‐quality surveys have confirmed the presence of hormones and antibiotics in surface waters of the United States, which may be of concern to aquatic life. We investigated the concentrations of hormones and antibiotics in surface waters of the state of Delaware to determine – how they compared against environmental thresholds, how they varied across the state, and if they were correlated with land use type. Fifty surface water locations were sampled during early spring and late summer. Water samples were initially screened with ELISA followed by analysis with LC/MS/MS. The measured ranges of hormone concentrations were: 0‐3.71 ng/l for estrone, 0‐4.65 ng/l for estrone‐3‐sulfate, and 0‐6.27 ng/l for 17β‐estradiol. The measured ranges of antibiotics were: 0‐3.30 ng/l for sulfamerazine, 0‐10.74 ng/l for sulfamethoxazole, and 0‐2.29 ng/l for tetracycline. The predicted no‐effect concentration (PNEC) for estrone was exceeded for three samples and the PNEC for 17β‐estradiol was exceeded for 11 samples. In general, concentrations and detection frequencies were lower in the summer than the spring. The highest concentrations of hormones and antibiotics were spatially distributed in agricultural and urban areas; however, the correlations between land use type and the concentrations were weak. This study was the first statewide survey of hormones and antibiotics for Delaware and provided important baseline data on these emerging contaminants.     

PARTIAL DEFORESTATION AND SHORT-TERM AUTOCHTHONOUS ENERGY INPUT TO A SMALL NEW ENGLAND STREAM1

ABSTRACT: Autochthonous energy input, in the form of periphyton production and growth, was studied before and after partial logging of the watershed surrounding School Brook, a small tributary of the Aroostook River, Maine. Due to infection by the spruce budworm (Chiristoneura fumiferana), the buffer strip on one bank of the stream was logged and only limited riparian vegetation was left. Though impacts in subsequent years are unknown, the effect of the logging on the periphyton community was insignificant during the nine months following cutting, seemingly due to several factors. Because only 5 percent of the canopy was actually removed, the intensity of available light changed little. Small springs in the area helped maintain a stable thermal regime, and only a small portion of the low gradient watershed was actually logged. Consequently, the nutrients reaching the stream did not change. The relatively low concentrations of nitrates (< 0.3 mg/l) and phosphates (< 10 μg/l), both before and in the first nine months after logging, reflect the limited autochthonous input, thereby reducing the effect of this limited cutting on the stream community.     

The Role of Headwater Wetlands in Altering Streamflow and Chemistry in a Maine,USA Catchment1

Morley, Terry R., Andrew S. Reeve, and Aram J.K. Calhoun, 2011. The Role of Headwater Wetlands in Altering Streamflow and Chemistry in a Maine, USA Catchment. Journal of the American Water Resources Association (JAWRA) 1‐13. DOI: 10.1111/j.1752‐1688.2011.00519.x Abstract: Headwater wetlands, including hillside seeps, may contribute to downstream systems disproportionately to their relatively small size. We quantified the hydrology and chemistry of headwater wetlands in a central Maine, USA, catchment from 2003 to 2005 to determine their role in maintaining headwater streamflow and in affecting stream chemistry. A few of these headwater wetlands, commonly referred to as “seeps,” were characterized by relatively high groundwater discharge. During summer base flow, seeps were the primary source of surface water to the stream, contributing between 40 and 80% of stream water. Comparisons of groundwater and surface water dominant ion chemistry revealed only slight differences at the bedrock interface; however, significant changes occurred at the shallow groundwater‐surface water interface where we found decreases in total and individual cation concentrations with decreasing depth. Seep outflows significantly increased total cation and calcium concentrations in streams. Outflows at two seeps produced relatively high nitrate concentrations (88 ± 15 and 93 ± 15 μg/l respectively), yet did not correspond to higher nitrate in stream water below seep outflows (2 ± 1 μg/l). We demonstrate that small wetlands (< 1,335 m²) can contribute to headwater stream processes by linking groundwater and surface‐water systems, increasing the duration and magnitude of stream discharge, and by affecting stream chemistry, particularly during periods of base flow.     

SMALL FISH MODELS FOR IDENTIFYING CARCINOGENS IN THE AQUEOUS ENVIRONMENT1

ABSTRACT: Contaminants in water and sediments can be carcinogenic to aquatic wildlife as well as humans. Identifying those carcinogens, however, is difficult because they often occur in low concentrations and exert their effects over a large part of the life span of affected organisms. Furthermore, the carcinogens are often components of complex mixtures. Recent studies suggest that laboratory-reared fish species might be well suited for testing water-associated and other carcinogens. Here, we review the principal carcinogen exposure methods that utilize small fish species or can be adapted to utilize small fish species to detect carcinogens in aqueous environments. Emphasis is placed on methods for which the end-point is tumor induction. The methods discussed are dietary exposures, skin painting, embryo microinjection, early life stage (pulse) exposures, static water exposures, flow-through exposures, and controlled field exposures. Early life stage exposures seem to have the greatest utility with regard to carcinogen sensitivity, ease of administration, disposal of test compounds, and economy of materials and effort. For certain types of carcinogens, however, long-term flow-through exposures are probably required. In summary, small fish carcinogenesis models offer an array of methodologies that can be utilized in a variety of combinations depending on compounds tested, exposure parameters employed, and end points sought.     

Physical and ecological thresholds for deposited sediments in streams in agricultural landscapes

Excessive sedimentation in streams and rivers remains a pervasive problem for the protection of aquatic habitat and the sustainability of aquatic communities. Whereas water quality criteria have been determined for suspended sediments in many jurisdictions across North America, comparably little has been done for deposited (also known as bedded) sediments. Through Canada's National Agri-Environmental Standards Initiative, assessment techniques and analytical tools were developed for estimating environmental thresholds for deposited sediments in agricultural watersheds in New Brunswick (NB) and Prince Edward Island (PEI) in the Atlantic Maritimes of Canada. Physical thresholds were developed through assessment of geomorphic metrics, which were then analyzed using y-intercept and 25th percentile approaches. For NB, there was strong agreement in physical thresholds for both analytical approaches (e.g., percent fines <2 mm were 7.5 for y-intercept and 6.9 for 25th percentile approaches). In contrast, physical thresholds for PEI differed considerably between approaches (e.g., percent fines <2 mm were 6.1 for y-intercept and 19.6 for 25th percentile approaches), likely due to a narrower range in agricultural land cover. Cross-calibration of our provisional physical thresholds for NB with ecological (i.e., benthic macroinvertebrate) assessments show that ecological thresholds, calculated as change-points in relationships between Ephemeroptera-Plecoptera-Trichoptera relative abundance or Modified Family Biotic Index and geomorphic criteria, were more liberal than physical thresholds. These results suggest that provisional thresholds developed using geomorphic criteria should demarcate change from the least disturbed condition and reduce the risk of sedimentation degrading benthic ecosystems.     

The littoral zone of lake okeechobee as a source of phosphorus after drawdown

Following a period of prolonged drought or intentional lake level drawdown, large littoral areas that once contained submersed aquatic vegetation (SAV) are reinundated when lake levels rise. A complete assessment of the contribution made by decomposing SAV to the in-lake phosphorus (P) concentration is important in both the management of Lake Okeechobee and understanding basic P processes. The P contribution to the open waters of Lake Okeechobee from a rapid inundation of exposed SAV was calculated by four methods: cores of field-desiccated SAV, cores of lab-desiccated SAV in the presence and absence of sediments, in situ decomposition, and sequential macrophyte harvesting. P releases, given such an episodic event, were similar among the four methods, ranging from 116±48 to 384±528 mg/m² in the absence of sediment. When SAV is in contact with sediment, which is the realistic field situation, the amount of P released was four times less (30±14 mg/m²) than in the absence of sediment. The calculated P releases would result in total P concentration increases in the lake from 2 to 15 μg/liter (upper 95% CI=2–25 μg/liter) in the absence of sediment; only 1 μg/liter increase was predicted when SAV released P in contact with sediment. Thus it is unlikely that a significant rise in total P concentrations in the limnetic zone of the lake would occur from the export of P released during the desiccation of SAV in the littoral-marsh zone during a drawdown.