Developing Nutrient Criteria for Streams: An Evaluation of the Frequency Distribution Method1

Abstract: The U.S. Environmental Protection Agency recommends two statistical methods to States and Tribes for developing nutrient criteria. One establishes a criterion as the 75th percentile of a reference‐population frequency distribution, the other uses the 25th percentile of a general‐population distribution; the U.S. Environmental Protection Agency suggests either method results in similar criteria. To evaluate each method, the Montana Department of Environmental Quality (MT DEQ) assembled data from STORET and other sources to create a nutrient general population. MT DEQ’s reference‐stream project provided reference population data. Data were partitioned by ecoregions, and by seasons (winter, runoff, and growing) defined for the project. For each ecoregion and season, nutrient concentrations at the 75th percentile of the reference population were matched to their corresponding concentrations in the general population. Additionally, nutrient concentrations from five regional scientific studies were matched to their corresponding reference population concentrations; each study linked nutrients to impacts on water uses. Reference‐to‐general population matches were highly variable between ecoregions, as nutrients at the 75th percentile of reference corresponded to percentiles ranging from the 4th to the 97th of the general population. In contrast, case studies‐to‐reference matches were more consistent, matching on average to the 86th percentile of reference, with a coefficient of variation of 13%.     

Nutrient Enrichment and Fish Nutrient Tolerance: Assessing Biologically Relevant Nutrient Criteria1

Abstract: Relationships between nutrient concentrations and fish nutrient tolerance were assessed relative to established nutrient criteria. Fish community, nitrate plus nitrite (nitrate), and total phosphorus (TP) data were collected during summer low‐flow periods in 2003 and 2004 at stream sites along a nutrient‐enrichment gradient in an agricultural basin in Indiana and Ohio and an urban basin in the Atlanta, Georgia, area. Tolerance indicator values for nitrate and TP were assigned for each species and averaged separately for fish communities at each site (TIV_o). Models were used to predict fish species expected to occur at a site under minimally disturbed conditions and average tolerance indicator values were determined for nitrate and TP separately for expected communities (TIV_e). In both areas, tolerance scores (TIV_o/TIV_e) for nitrate increased significantly with increased nitrate concentrations whereas no significant relationships were detected between TP tolerance scores and TP concentrations. A 0% increase in the tolerance score (TIV_o/TIV_e = 1) for nitrate corresponded to a nitrate concentration of 0.19 mg/l (compared with a USEPA summer nitrate criterion of 0.17 mg/l) in the urban area and 0.31 mg/l (compared with a USEPA summer nitrate criterion of 0.86 mg/l) in the agricultural area. Fish nutrient tolerance values offer the ability to evaluate nutrient enrichment based on a quantitative approach that can provide insights into biologically relevant nutrient criteria.     

Compensatory Mitigation for Streams Under the Clean Water Act: Reassessing Science and Redirecting Policy1

Doyle, Martin W. and F. Douglas Shields, 2012. Compensatory Mitigation for Streams Under the Clean Water Act: Reassessing Science and Redirecting Policy. Journal of the American Water Resources Association (JAWRA) 48(3): 494-509. DOI: 10.1111/j.1752-1688.2011.00631.x Abstract: Current stream restoration science is not adequate to assume high rates of success in recovering ecosystem functional integrity. The physical scale of most stream restoration projects is insufficient because watershed land use controls ambient water quality and hydrology, and land use surrounding many restoration projects at the time of their construction, or in the future, do not provide sufficient conditions for functional integrity recovery. Reach scale channel restoration or modification has limited benefits within the broader landscape context. Physical habitat variables are often the basis for indicating success, but are now increasingly seen as poor surrogates for actual biological function; the assumption “if you build it they will come” lacks support of empirical studies. If stream restoration is to play a continued role in compensatory mitigation under the United States Clean Water Act, then significant policy changes are needed to adapt to the limitations of restoration science and the social environment under which most projects are constructed. When used for compensatory mitigation, stream restoration should be held to effectiveness standards for actual and measurable physical, chemical, or biological functional improvement. To achieve improved mitigation results, greater flexibility may be required for the location and funding of restoration projects, the size of projects, and the restoration process itself.     

Tributary Plunging in an Urban Lake (Onondaga Lake): Drivers,Signatures, and Implications1

Abstract: A combination of long‐term fixed‐frequency and robotic monitoring information for a polluted urban lake, Onondaga Lake, New York, and two of its tributaries is used to resolve the propensity for, and occurrences of, tributary plunging. Cooler temperatures (T) and higher salinity (S) are primarily responsible for the elevated density and plunging of one of these polluted streams for the summer through early fall interval. In‐lake transport of this plunging tributary, which receives inputs from combined sewer overflows (CSOs), is tracked by its high S during dry weather, its high turbidity (T_n) with associated lower S (dilution with rainwater) following runoff events, and by its characteristic ionic composition. These signatures are documented extending from the creek mouth, through a connecting navigation channel, through the inflow zone of the lake, and into metalimnetic depths of pelagic portions of the lake. The entry of this polluted tributary below the depth interval(s) of primary production and contact recreation has important implications for the ongoing major rehabilitation program for this lake. The plunging phenomenon diminishes the benefits previously expected for related features of the lake’s water quality from ongoing management efforts to abate CSO inputs and reduce nonpoint nutrient loading from the tributary. Previously this tributary tended to instead enter the upper layers of the lake during the operation of an adjoining soda ash manufacturing facility (closure in 1986), as a result of high lake S caused by the industry’s ionic waste discharge.     

A Regional‐Scale Habitat Suitability Model to Assess the Effects of Flow Reduction on Fish Assemblages in Michigan Streams1

Zorn, Troy G., Paul W. Seelbach, and Edward S. Rutherford, 2012. A Regional‐Scale Habitat Suitability Model to Assess the Effects of Flow Reduction on Fish Assemblages in Michigan Streams. Journal of the American Water Resources Association (JAWRA) 48(5): 871‐895. DOI: 10.1111/j.1752‐1688.2012.00656.x Abstract: In response to concerns over increased use and potential diversion of Michigan’s freshwater resources, and the resulting state legislative mandate, an advisory council created an integrated assessment model to determine the potential for water withdrawals to cause an adverse resource impact to fish assemblages in Michigan’s streams. As part of this effort, we developed a model to predict how fish assemblages characteristic of different stream types would change in response to decreased stream base flows. We describe model development and use in this case study. The model uses habitat suitability information (i.e., catchment size, base‐flow yield, and July mean water temperature) for over 40 fish species to predict assemblage structure in an individual river segment under a range of base‐flow reductions. By synthesizing model runs for individual fish species at representative segments for each of Michigan’s 11 ecological stream types, we developed curves describing how typical fish assemblages in each type respond to flow reduction. Each stream type‐specific, fish response curve was used to identify streamflow reduction levels resulting in adverse resource impacts to characteristic fish populations, the regulatory standard. Used together with a statewide map of stream types, our model provided a spatially comprehensive framework for evaluating impacts of flow withdrawals on biotic communities across a diverse regional landscape.     

Modeling Biochemical Oxygen Demand Through the Middle and Lower Savannah River1

Abstract: In order to improve modeling accuracy and general understanding of lotic biochemical oxygen demand (BOD), this study characterized river metabolism with the current Georgia Environmental Protection Division method for the middle and lower Savannah River basin (MLSRB) and several alternative methods developed with 120‐day, long‐term biochemical oxygen demand (LTBOD) data from the MLSRB. The data were a subset of a larger two‐year LTBOD study to characterize and understand BOD in the MLSRB, located approximately between Augusta, Georgia, and Savannah, Georgia, along the border of Georgia and South Carolina. The LTBOD data included total oxygen loss and nitrogen speciation for separately quantifying nitrification. Results support the following insights and opportunities for modeling methods: (1) it is important to modeling accuracy that residuals be checked for even dispersion to avoid areas of over‐ and underprediction; (2) modeling with bounded, yet unfixed, rates is a sufficiently simple alternative to fixed‐rate modeling that can eliminate the need for manual adjustments and provide additional system understanding to inform regulation; (3) if fixed rates modeling is desired, model quality for this system might be improved through revising the current low rate (along with the associated f‐ratio updates) from 0.02/day rate to 0.006/day and potentially adding a new rate at 1.0/day in some cases; and (4) the current 57/43 ratio of slow/fast BOD is reasonable based on the 52/45/3 slow/fast/faster BOD proportions of this study.     

A Multi‐Agency Nutrient Dataset Used to Estimate Loads,Improve Monitoring Design,and Calibrate Regional Nutrient SPARROW Models1

Saad, David A., Gregory E. Schwarz, Dale M. Robertson, and Nathaniel L. Booth, 2011. A Multi‐Agency Nutrient Dataset Used to Estimate Loads, Improve Monitoring Design, and Calibrate Regional Nutrient SPARROW Models. Journal of the American Water Resources Association (JAWRA) 47(5):933‐949. DOI: 10.1111/j.1752‐1688. 2011.00575.x Abstract: Stream‐loading information was compiled from federal, state, and local agencies, and selected universities as part of an effort to develop regional SPAtially Referenced Regressions On Watershed attributes (SPARROW) models to help describe the distribution, sources, and transport of nutrients in streams throughout much of the United States. After screening, 2,739 sites, sampled by 73 agencies, were identified as having suitable data for calculating long‐term mean annual nutrient loads required for SPARROW model calibration. These sites had a wide range in nutrient concentrations, loads, and yields, and environmental characteristics in their basins. An analysis of the accuracy in load estimates relative to site attributes indicated that accuracy in loads improve with increases in the number of observations, the proportion of uncensored data, and the variability in flow on observation days, whereas accuracy declines with increases in the root mean square error of the water‐quality model, the flow‐bias ratio, the number of days between samples, the variability in daily streamflow for the prediction period, and if the load estimate has been detrended. Based on compiled data, all areas of the country had recent declines in the number of sites with sufficient water‐quality data to compute accurate annual loads and support regional modeling analyses. These declines were caused by decreases in the number of sites being sampled and data not being entered in readily accessible databases.     

How Green is Too Green? Public Opinion of What Constitutes Undesirable Algae Levels in Streams1

Abstract: A public opinion survey was carried out in Montana to ascertain if the public identifies a level of benthic (bottom‐attached) river and stream algae that is undesirable for recreation. The survey had two parts; an On‐River survey and a By‐Mail survey. The On‐River survey was conducted via 44 trips randomly scheduled throughout the state during which recreators were interviewed in‐person at the stream. Selection of stream segments and survey dates/times was based on known, statewide recreational use patterns. By‐Mail survey forms were sent to 2,000 individuals randomly selected from Montana’s Centralized Voter File (CVF) available from the Montana Secretary of State. The CVF was current through 2004 and represented over 85% of the state’s eligible voting population. In both surveys, eight randomly ordered photographs depicting varying levels of stream benthic algae were presented, and participants were asked if the algae level shown was desirable or undesirable for recreation. Survey form design, selection of photographs, and pretesting followed acceptable protocols that limited unintentional bias through survey execution. There were 433 returned forms (389 complete) for the By‐Mail survey, while the On‐River survey documented 563 interviews. In both surveys, as benthic algal chlorophyll a (Chl a) levels increased, desirability for recreation decreased. (Other measures of benthic algae biomass are presented as well.) For the public majority, mean benthic Chl a levels ≥200 mg/m² were determined to be undesirable for recreation, whereas mean levels ≤150 mg Chl a/m² were found to be desirable. Error rates were within the survey’s statistical design criteria (≤5%). The largest potential error source was nonresponse in the By‐Mail survey; however, the population represented by nonrespondents would have to exhibit profoundly different perceptions of river and stream algae to meaningfully alter the results. Results support earlier work in the literature suggesting 150 mg Chl a/m² represents a benthic algae nuisance threshold.     

Ecosystem Consequences of Contrasting Flow Regimes in an Urban Effects Stream Mesocosm Study1

Abstract: A stream mesocosm experiment was conducted to study the ecosystem‐wide effects of two replicated flow hydrograph treatments programmed in an attempt to compare a simulated predevelopment condition to the theoretical changes that new development brings, while accounting for engineering design criteria for urban stormwater management. Accordingly, the treatments (three replicates each) differed in base flow between events and in the rise to, fall from, and duration of peak flow during simulated storm hydrographs, which were triggered by real rain events occurring outside over a 96‐day period from summer to fall, 2005. Incident irradiance, initial substrate quality, and water quality were similar between treatments. Sampling was designed to study the interactions among the treatment flow dynamics, sediment transport processes, streambed nutrients, and biotic structure and function. What appeared most important to the overall structure and function of the mesocosm ecosystems beyond those changes resulting from natural seasonality were (1) the initial mass of fines that infiltrated into the gravel bed, which had a persistent effect on nitrogen biogeochemistry and (2) the subsequent fine sediment accumulation rate, which was unexpectedly similar between treatments, and affected the structure of the macroinvertebrate community equally as the experiment progressed. Invertebrate taxa preferring soft beds dominated when the gravel was comprised of 5‐10% fines. The dominant invertebrate algal grazer had vacated the channels when fines exceeded 15%, but this effect could not be separated from what appeared to be a seasonal decline in insect densities over the course of the study. Neither hydrograph treatment allowed for scour or other potential for flushing of fines. This demonstrated the potential importance of interactions between hydrology and fine sediment loading dynamics on stream ecosystems in the absence of flows that would act to mobilize gravel beds.     

Surface‐Water Nutrient Conditions and Sources in the United States Pacific Northwest1

Wise, Daniel R. and Henry M. Johnson, 2011. Surface‐Water Nutrient Conditions and Sources in the United States Pacific Northwest. Journal of the American Water Resources Association (JAWRA) 47(5):1110‐1135. DOI: 10.1111/j.1752‐1688.2011.00580.x Abstract: The SPAtially Referenced Regressions On Watershed attributes (SPARROW) model was used to perform an assessment of surface‐water nutrient conditions and to identify important nutrient sources in watersheds of the Pacific Northwest region of the United States (U.S.) for the year 2002. Our models included variables representing nutrient sources as well as landscape characteristics that affect nutrient delivery to streams. Annual nutrient yields were higher in watersheds on the wetter, west side of the Cascade Range compared to watersheds on the drier, east side. High nutrient enrichment (relative to the U.S. Environmental Protection Agency’s recommended nutrient criteria) was estimated in watersheds throughout the region. Forest land was generally the largest source of total nitrogen stream load and geologic material was generally the largest source of total phosphorus stream load generated within the 12,039 modeled watersheds. These results reflected the prevalence of these two natural sources and the low input from other nutrient sources across the region. However, the combined input from agriculture, point sources, and developed land, rather than natural nutrient sources, was responsible for most of the nutrient load discharged from many of the largest watersheds. Our results provided an understanding of the regional patterns in surface‐water nutrient conditions and should be useful to environmental managers in future water‐quality planning efforts.