Hydrobiogeochemical Controls on Riparian Nutrient and Greenhouse Gas Dynamics: 10 Years Post‐Restoration

Little is known about the impact of agricultural legacy on subsurface biogeochemical processes in the years following restoration of riparian wetlands (WLs). More knowledge is also needed on the relative importance of seasons, precipitation events, and inputs of water and nutrients driving nitrogen (N), phosphorus (P), sulfur (S), and greenhouse gas (GHG) (N₂O, CO₂, CH₄) dynamics in these systems. This investigation of a riparian zone comprising a restored WL area and a nonrestored well‐drained alluvium (AL) area in the United States Midwest revealed that despite successful hydrological restoration a decade earlier, biogeochemical conditions in the WL area remained less anoxic than in natural WLs, and not significantly different from those in the AL area. No significant differences in N, P, S, and C compound concentrations or fluxes were observed between the AL and WL areas. Over the duration of the study, nitrate (NO₃^?) and soluble reactive phosphorus appeared to be primarily driven by hillslope contributions. Ammonium (NH₄⁺), sulfate (SO₄^2?), and CO₂ responded strongly to seasonal changes in biogeochemical conditions in the riparian zone, while N₂O and CH₄ fluxes were most influenced by large rewetting events. Overall, our results challenge overly simplistic assumptions derived from direct interpretation of redox thermodynamics, and show complex patterns of solutes and GHGs at the riparian zone scale.     

Nutrient Removal and Loading Rate Analysis of Louisiana Forested Wetlands Assimilating Treated Municipal Effluent

The relationship between nutrient removal and loading rate was examined using data from five forested wetlands in Louisiana that have received secondarily treated effluent from 3 to 60 years. Loading rates ranged from 0.65 to 26.80 g/m²/yr for total nitrogen and 0.18 to 8.96 g/m²/yr for total phosphorus. At loading rates below 20 g/m²/yr, total nitrogen concentrations in surface waters of Louisiana forested wetlands were reduced to background concentrations (i.e., ≤3 mg/l). Similarly, at loading rates below 2 g/m²/yr, total phosphorus concentrations were also generally reduced to background concentrations (i.e., ≤1 mg/l). These data demonstrate that freshwater forested wetlands can reduce nutrient concentrations in treated effluent to background concentrations present in relatively undisturbed wetlands. An understanding of the relationship between loading rates and nutrient removal in natural wetlands is important, particularly in Louisiana where discharges of fresh water are being used in ecosystem restoration.     

Role of Riparian Areas in Atmospheric Pesticide Deposition and Its Potential Effect on Water Quality

Riparian buffers are known to mitigate hydrologic losses of nutrients and other contaminants as they exit agricultural fields. The vegetation of riparian buffers can also trap atmospheric contaminants, and these pollutants can subsequently be delivered via rain to the riparian buffer floor. These processes, however, are poorly understood especially for pesticide residues. Therefore, we conducted a four‐year study examining stemflow and throughfall to a riparian buffer which was adjacent a cultured Zea mays field treated with atrazine and metolachlor. Stemflow is rain contacting the tree canopy traveling down smaller to larger branches and down the tree trunk, whereas throughfall is rain that may or may not contact leaves and branches and reaches the earth. Stemflow concentrations of the herbicides were larger than throughfall concentrations and accounted for 5‐15% of the atrazine and 6‐66% of the metolachlor depositional fluxes under the canopy. Larger depositional fluxes were measured when leaves were more fully emerged and temperatures and humidity were elevated. Rain collected outside the riparian buffer on the field side and on the back side revealed the trees trapped the herbicide residues. Herbicide loading to the riparian buffer stream was found to be linked to tree canopy deposition and subsequent washoff during rain events. These results indicate that in agricultural areas canopy washoff can be an important source of pesticides to surface waters.     

DO WETLANDS BEHAVE LIKE SHALLOW LAKES IN TERMS OF PHOSPHORUS DYNAMICS?1

ABSTRACT: The applicability of empirical relationships governing phosphorus (P) retention and nutrient assimilation in lakes and reservoirs was extended to include free surface water wetland treatment systems. Mixed reactor models have been used in lakes to predict steady state P concentration, characterize trophic state, compare P‐dynamics, and predict permissible P‐loading rates. Applying lake models to free surface water wetlands treatment systems, it was found that: sedimentation rates, loading rates, and settling velocity in these wetlands, and their typology are comparable to their lake counterparts. The analyses also suggest that phosphorus removal efficiency in a free surface water wetland treatment system is independent of trophic status, and similar to lakes, these wetlands can be classified according to their trophic state. Oligo‐and eutrophic wetland treatment systems can be defined by low and high TP inflow concentrations, respectively. In this study, olig‐otrophic status is defined as systems receiving inflow P‐loading less than 0.10 g m^‐2 year‐¹, and their P inputs are mainly derived from agricultural and stormwater runoff. Eutrophic treatment systems, on the other hand, are defined as those receiving inflow P‐loading higher than 0.20 g m² year‐¹, and their inputs are mainly derived from industrial and municipal wastewater. The comparability found between lakes and free surface water wetlands treatment systems raises the question: should we consider these wetlands “shallow lakes?”     

Mitigation of shallow groundwater nitrate in a poorly drained riparian area and adjacent cropland

Riparian ecosystems, through their unique position in the agricultural landscape and ability to influence nutrient cycles, can potentially reduce NO3 loading to surface and ground waters. The purpose of this study was to determine the fate of NO3 in shallow groundwater moving along a lateral flowpath from a grass seed cropping system through an undisturbed mixed-species herbaceous riparian area. Soil A (30-45 cm) and C horizon (135-150 cm) NO3, dissolved oxygen, and nitrous oxide concentrations were significantly higher in the cropping system than the adjacent riparian area. Nitrate concentrations in both horizons of the riparian soil were consistently at or below 0.05 mg N L(-1) while cropping system concentrations ranged from 1 to 12 mg N L(-1). Chloride data suggested that NO3 dilution occurred from recharge by precipitation. However, a sharp decrease in NO3/Cl ratios as water moved into the riparian area indicated that additional dilution of NO3 concentrations was unlikely. Riparian area A horizon soil water had higher dissolved organic carbon than the cropping system and when the riparian soil became saturated, available electron acceptors (O2, NO3) were rapidly reduced. Dissolved inorganic carbon was significantly higher in the riparian area than the cropping system for both horizons indicating high biological activity. Carbon limitation in the cropping system may have led to microbial respiration using primarily O2 and to a lesser degree NO3. Within 6 m of the riparian/cropping system transition, NO3 was virtually undetectable.     

A Geospatial Methodology to Identify Locations of Concentrated Runoff from Agricultural Fields

A geospatial methodology has been developed that utilizes high resolution lidar‐derived DEMs to help track runoff from agricultural fields and identify areas of potential concentrated flow through vegetated riparian areas in the Coastal Plain of Virginia. Points of concentrated flow are identified across 74 agricultural fields within the Virginia portion of the Chesapeake Bay watershed. On average, 70% of the surface area of the agricultural fields analyzed drains through less than 20 m of the field margin, and on average 81% of the field surface area drains through 1% or less of the field margin. Within the riparian buffer, locations that were predicted by the geospatial model to have high levels of concentrated flow were found to exhibit evidence of channelization. Results indicate that flow concentration and channelized flow through vegetated riparian areas may be common along the margin of agricultural fields, resulting in vegetated riparian areas that are less effective at sediment trapping than assumed. Additional results suggest that the regulations governing the location and width of vegetated riparian may not be sufficient to achieve goals for reducing sediment and nutrient runoff from nonpoint agricultural sources. Combined with the increasing availability of lidar‐derived DEMs, the geospatial model presented has the potential to advance management practices aimed at reducing nonpoint source pollution leaving agricultural fields.     

NONPOINT SOURCE POLLUTION POTENTIAL IN AN AGRICULTURAL WATERSHED IN NORTHWESTERN PENNSYLVANIA1

ABSTRACT: A 155,947 ha portion of the Shenango River watershed in western Pennsylvania was evaluated as to the potential impact of agriculture drainage on water quality. Approximately a third of the area is being used as either cropland or pasture with approximately an equal percentage in forest lands. Eleven subwatersheds were evaluated as to their potential for nonpoint source pollution according to the criteria established by the Pennsylvania Department of Environmental Resources for the Chesapeake Bay Pollution Abatement Program. The individual components and overall rating for each subwatershed were then evaluated as to their correlation with four water quality variables based on 104 samples collected at 26 sampling stations throughout the watershed. There was a significant correlation between the overall rating factor for each subwatershed and each of the four water quality variables. In general, the watershed delivery factor, animal nutrient factor, and management factors were correlated with fecal coliform and phosphorus in the receiving streams, whereas the ground water delivery factor appeared to be more important in determining nitrate concentrations in these streams. These results indicate that manure and nutrient management, along with the exclusion of livestock from streams and the enhancement and/or replacement of riparian wetlands, are important approaches in reducing agricultural impacts in fresh water ecosystems.     

Reducing sediment and phosphorus in tributary waters with alum and polyacrylamide

The Salton Sea is the largest inland water body in California, covering an area of 980 km(2). Inflow to the Salton Sea (1.6 km(3) yr(-1)) is predominately nutrient-rich agricultural wastewater, which has led to eutrophication. Because internal phosphorus release from the bottom sediments is comparatively low and external phosphorus loading to the Salton Sea is high, reduction of tributary phosphorus is expected to reduce algal blooms, increase dissolved oxygen, and reduce odors. Removing both dissolved phosphorus and phosphorus-laden sediment from agricultural drainage water (ADW) should decrease eutrophication. Both alum and polyacrylamide (PAM) are commonly used in wastewater treatment to remove phosphorus and sediment and were tested for use in tributary waters. Laboratory jar tests determined PAM effectiveness (2 mg L(-1)) for turbidity reduction as cationic > anionic = nonionic. Although cationic PAM was the most effective at reducing turbidity at higher speeds, there was no observed difference between the neutral and anionic PAMs at velocity gradients of 18 to 45 s(-1). Alum (4 mg L(-1) Al) reduced turbidity in low energy systems (velocity gradients < 10 s(-1)) by 95% and was necessary to reduce soluble phosphorus, which comprises 47 to 100% of the total P concentration in the tributaries. When PAM was added with alum, the anionic PAM became ineffective in aiding flocculation. The nonionic PAM (2 mg L(-1)) + alum (4 mg L(-1) Al) is recommended to reduce suspended solids in higher energy systems and reduce soluble P by 93%.     

LONG-TERM EQUILIBRIUM PHOSPHORUS CONCENTRATIONS IN THE EVERGLADES AS PREDICTED BY A VOLLENWEIDER-TYPE MODEL1

ABSTRACT: Anthropogenic phosphorus loading, mainly from the Everglades Agricultural Area (EAA), is believed to be the primary cause of eutrophication in the Everglades. The state of Florida has adopted a plan for addressing Everglades eutrophication problems by reducing anthropogenic phosphorus loads through the implementation of Best Management Practices (BMPs) in agricultural watersheds and the construction of stormwater treatment areas (STAs). Optimizing the effectiveness of these STAs for reducing phosphorus concentrations from agricultural runoff is a critical component of the District's comprehensive Everglades protection effort. Therefore, the objective of this study was to develop a simple tool that can be used to estimate STAs’performance and evaluate management alternatives considered in the Everglades restoration efforts. The model was tested at two south Florida wetland sites and then was used to simulate several management alternatives and predict ecosystem responses to reduced external phosphorus (P) loadings. Good agreement between model predictions at the two wetland sites and actual observations indicated that the model can be used as a management tool to predict wetlands’response to reductions in external phosphorus load and long-term P levels in aquatic ecosystems. Model results showed that lowering P content of the Everglades Protection Area (EPA) depends on reducing P loads originating from EAA discharges, not from rainfall. Assuming no action is taken (e.g., no BMPs or STAs implemented), the steady state model predicted that the average concentration within the modeled area of the marsh would reach 20 μg L^?1 within five years. With an 85 percent reduction in P loading, the steady-state model predicted that Water Conservation Area 2A (WCA-2A) P concentration will equilibrate at approximately 10 μ L^?1, while elimination of all loadings is projected to further reduce marsh P to values less than 10 μg L^?1.     

Relative Importance of Water‐Quality Stressors in Predicting Fish Community Responses in Midwestern Streams

Fish, habitat, and water chemistry data were collected from 98 streams in the midwestern United States, an area dominated by intense cultivation of row crops, in order to identify important water‐quality stressors to fish communities. We focused on 10 stressors including riparian disturbance, riparian vegetative cover, instream fish cover, streambed sedimentation, streamflow variability, total nitrogen, total phosphorus, minimum dissolved oxygen, pesticides, and bed sediment contaminants. Fish community response variables included a measure of observed/expected taxonomic completeness; species‐specific tolerances to nitrogen, phosphorus, dissolved oxygen, and water temperature; the percent of species classified as macrohabitat generalists; and an index of pesticide toxicity to fish. Multivariate analysis indicated that total nitrogen was the most important stressor, signifying that fish communities were responding to total nitrogen despite relatively high levels common to an agricultural setting. Individually, fish taxonomic completeness decreased with increasing streambed sedimentation, whereas fish community tolerance to total phosphorus increased with increasing streambed sedimentation, riparian disturbance, and total nitrogen. These findings underscore the importance of multiple biological response metrics to better understand the effects of water‐quality stressors on fish communities and highlight the complex relations between total phosphorus and fish communities.     

Can constructed wetlands reduce the diffuse phosphorus loads to eutrophic water in cold temperate regions?

Construction of wetlands is a possible supplement to best management practices (BMP) at the field level to mitigate phosphorus (P) pollution from agricultural areas. In this paper, annual results from 17 intensively studied wetlands in the cold temperate or boreal climatic zone are reported and analyzed. Surface areas varied from 0.007 to 8.7% of the catchment area. The average total phosphorus (TP) retention varied from 1 to 88%, and the dissolved reactive phosphorus (DRP) retention from -19 to 89%. Retention varied substantially from site to site, indicating the existence of site-specific factors in the catchment and wetlands that influenced the P removal. Factors important for P retention in wetlands were evaluated through multiple statistical analyses by dividing P into two fractions: particulate phosphorus (PP) and DRP. Both relative (%) PP and DRP retention increased with wetland surface area. However, PP retention was not as sensitive as DRP in terms of wetland size and retention: specific PP retention (gram P retention per m(2) and year) decreased as wetland area (A(w)) increased, suggesting the existence of a site-specific optimal wetland to catchment area (A(c)) ratio. Particulate P retention decreased with increasing DRP to TP ratio, while the opposite was found for DRP. Dissolved reactive P retention was higher in new than in old wetlands, while increasing age did not influence PP retention negatively. Effective BMP in the catchment is important to keep the P loss low, because the outlet concentration of P from wetlands is often positively correlated to the input concentration. However, wetlands act as the last buffer in a catchment, since the retention often increases as the P concentration in streams increases.     

Phosphorus losses from agricultural areas in river basins: effects and uncertainties of targeted mitigation measures

In this paper we show the quantitative and relative importance of phosphorus (P) losses from agricultural areas within European river basins and demonstrate the importance of P pathways, linking agricultural source areas to surface water at different scales. Agricultural P losses are increasingly important for the P concentration in most European rivers, lakes, and estuaries, even though the quantity of P lost from agricultural areas in European catchments varies at least one order of magnitude (<0.2 kg P ha(-1) to >2.1 kg P ha(-1)). We focus on the importance of P for the implementation of the EU Water Framework Directive and discuss the benefits, uncertainties, and side effects of the different targeted mitigation measures that can be adopted to combat P losses from agricultural areas in river basins. Experimental evidence of the effects of some of the main targeted mitigation measures hitherto implemented is demonstrated, including: (i) soil tillage changes, (ii) treatment of soils near ditches and streams with iron to reduce P transport from source areas to surface waters, (iii) establishment of buffer zones for retaining P from surface runoff, (iv) restoration of river-floodplain systems to allow natural inundation of riparian areas and deposition of P, and (v) inundation of riparian areas with tile drainage water for P retention. Furthermore, we show how river basin managers can map and analyze the extent and importance of P risk areas, exemplified by four catchments differing in size in Norway, Denmark, and the Netherlands. Finally, we discuss the factors and mechanisms that may delay and/or counteract the responses of mitigation measures for combating P losses from agricultural areas when monitored at the catchment scale.     

Recent Land Cover History and Nutrient Retention in Riparian Wetlands

Wetland ecosystems are profoundly affected by altered nutrient and sediment loads received from anthropogenic activity in their surrounding watersheds. Our objective was to compare a gradient of agricultural and urban land cover history during the period from 1949 to 1997, with plant and soil nutrient concentrations in, and sediment deposition to, riparian wetlands in a rapidly urbanizing landscape. We observed that recent agricultural land cover was associated with increases in Nitrogen (N) and Phosphorus (P) concentrations in a native wetland plant species. Conversely, recent urban land cover appeared to alter receiving wetland environmental conditions by increasing the relative availability of P versus N, as reflected in an invasive, but not a native, plant species. In addition, increases in surface soil Fe content suggests recent inputs of terrestrial sediments associated specifically with increasing urban land cover. The observed correlation between urban land cover and riparian wetland plant tissue and surface soil nutrient concentrations and sediment deposition, suggest that urbanization specifically enhances the suitability of riparian wetland habitats for the invasive species Japanese stiltgrass [Microstegium vimenium (Trinius) A. Camus].     

Effectiveness of Constructed Overland Flow Areas in Decreasing Diffuse Pollution from Forest Drainages

Forestry is the largest scale human impact affecting catchments in Finland and a prominent source of diffuse pollution in many water courses. Among the forestry activities, draining of wetlands had the most pronounced impacts on sediment, nutrient, and metal loading in the past. At present, renovation of old ditches and fertilization of peatlands constitute the major risk of forestry-induced diffuse pollution. Contemporary forestry aims at decreasing this risk with various riparian buffer strip designs. Among such designs, creation of overland flow areas by plugging the outlet ditches is increasingly used. Our objectives were to evaluate the potential of constructed overland flow areas to function as riparian buffers and estimate the quality and quantity of diffuse pollution from old versus recent forest drainages. We studied retention and release of pollutants from 20 constructed, 2- to 10-m-wide overland flow areas receiving drainage water from forested peatlands. Drainage waters were sampled above and below the plugged ditches three times per year from 1998 to 1999. Chemical oxygen demand and nutrient and metal loads and concentrations varied strongly between seasons, years, and drainage areas. Areas subjected to recent ditch renovations and fertilizations had clearly elevated seasonal loads and concentrations of total phosphorus (TP), PO₄, Fe, and Al in comparison to old treatment areas. Especially TP loads were high above the national average values measured for forestry-induced diffuse pollution. In general, water quality above and below the buffer strips did not differ significantly. Our results indicate that plugged outlet ditches and associated narrow overland flow areas do not function as proper buffers in peatland areas. We suggest that wider buffers with extensive overland flow areas are needed in order to control diffuse pollution from forested and drained peatlands.     

Physical and Chemical Connectivity of Streams and Riparian Wetlands to Downstream Waters: A Synthesis

Streams, riparian areas, floodplains, alluvial aquifers, and downstream waters (e.g., large rivers, lakes, and oceans) are interconnected by longitudinal, lateral, and vertical fluxes of water, other materials, and energy. Collectively, these interconnected waters are called fluvial hydrosystems. Physical and chemical connectivity within fluvial hydrosystems is created by the transport of nonliving materials (e.g., water, sediment, nutrients, and contaminants) which either do or do not chemically change (chemical and physical connections, respectively). A substantial body of evidence unequivocally demonstrates physical and chemical connectivity between streams and riparian wetlands and downstream waters. Streams and riparian wetlands are structurally connected to downstream waters through the network of continuous channels and floodplain form that make these systems physically contiguous, and the very existence of these structures provides strong geomorphologic evidence for connectivity. Functional connections between streams and riparian wetlands and their downstream waters vary geographically and over time, based on proximity, relative size, environmental setting, material disparity, and intervening units. Because of the complexity and dynamic nature of connections among fluvial hydrosystem units, a complete accounting of the physical and chemical connections and their consequences to downstream waters should aggregate over multiple years to decades.     

Impact of flood control reservoirs and pollution influx on the Sandy Creek Watershed,Mercer County,Pennsylvania, USA

A study of the impact of two flood control reservoirs and pollution influx was conducted on two streams within the Sandy Creek Watershed, Mercer County, Pennsylvania, USA. Fecal coliforms were significantly reduced in the outflows without affecting water chemistry, thereby improving the overall water quality. The size and composition of the aquatic communities as well as stream metabolism varied seasonably among the different sampling stations. Pollution influx primarily from communities and agricultural drainage had a greater impact on the stream ecosystem than did impounding of the streams. Natural wetlands and riparian vegetation were important factors in reducing the pollution load in these streams. The reestablishment and maintenance of riparian vegetation should therefore be an integral part of the land-use plan for watersheds in order to improve water quality and wildlife habitats. In the future, the maintenance of riparian vegetation should be given prime consideration in the development of watershed projects.     

Evaluation of Progress in Achieving TMDL Mandated Nitrogen Reductions in the Neuse River Basin, North Carolina

Management efforts to control excess algal growth in the Neuse River and Estuary, North Carolina began in the 1980s, with an initial focus on phosphorus (P) input reduction. However, continued water quality problems in the 1990s led to development of a Total Maximum Daily Load (TMDL) for nitrogen (N) in 1999 to improve conditions in N-sensitive estuarine waters. Evaluation of the effectiveness of management actions implemented in the Neuse River basin is a challenging endeavor due to natural variations in N export associated with climate. A simplified approach is presented that allows evaluation of trends in flow-normalized nutrient loading to provide feedback on effectiveness of implemented actions to reduce N loading to estuarine waters. The approach is applied to five watershed locations, including the headwaters of the Neuse Estuary. Decreases in nitrate + nitrite (NO₃–N) concentrations occurred throughout the basin and were largest just downstream of the Raleigh metropolitan area. Conversely, concentrations of total Kjeldahl N (TKN) increased at many stations, particularly under high flow conditions. This indicates a relative increase in organic N (Org-N) inputs since the mid-1990s. Overall, patterns in different N fractions at watershed stations indicate both partial success in reducing N inputs and ongoing challenges for N loading under high flow conditions. In downstream waters, NO₃–N concentrations decreased concurrent with TMDL implementation in the upper portion of the estuary but not in the middle and lower reaches. The lack of progress in the middle and lower reaches of the estuary may, at least in part, be affected by remineralization of settled particle-bound N deposited under high river flows.     

Landscape Planning for Agricultural Nonpoint Source Pollution Reduction I: A Geographical Allocation Framework

Agricultural nonpoint source pollution remains a persistent environmental problem, despite the large amount of money that has been spent on its abatement. At local scales, agricultural best management practices (BMPs) have been shown to be effective at reducing nutrient and sediment inputs to surface waters. However, these effects have rarely been found to act in concert to produce measurable, broad-scale improvements in water quality. We investigated potential causes for this failure through an effort to develop recommendations for the use of riparian buffers in addressing nonpoint source pollution in Wisconsin. We used frequency distributions of phosphorus pollution at two spatial scales (watershed and field), along with typical stream phosphorus (P) concentration variability, to simulate benefit/cost curves for four approaches to geographically allocating conservation effort. The approaches differ in two ways: (1) whether effort is aggregated within certain watersheds or distributed without regard to watershed boundaries (dispersed), and (2) whether effort is targeted toward the most highly P-polluting fields or is distributed randomly with regard to field-scale P pollution levels. In realistic implementation scenarios, the aggregated and targeted approach most efficiently improves water quality. For example, with effort on only 10% of a model landscape, 26% of the total P load is retained and 25% of watersheds significantly improve. Our results indicate that agricultural conservation can be more efficient if it accounts for the uneven spatial distribution of potential pollution sources and the cumulative aspects of environmental benefits.     

TILE RATIONALE FOR OHIO'S DETERGENT PHOSPHORUS BAN1

ABSTRACT: Ohio signed into law a detergent phosphorus ban on March 26, 1988. This law limits the elemental phosphorus content of household laundry detergents to 0.5 percent in all 35 Lake Erie counties in Ohio by 1990. Ohio's detergent phosphorus ban will help non-compliant municipal wastewater treatment plants achieve compliance with the 1 mg/L effluent phosphorus standard. By limiting the phosphorus content of household laundry detergents, Ohio will also benefit from less phosphorus entering surface waters from combined sewer overflows, communities with treatment plant bypasses, and riparian homes with septic tanks. This is important because most of the phosphorus in laundry detergents is in the bioavailable form and Ohio's Lake Erie shoreline is particularly sensitive to Cladophora problems. When viewed in conjunction with reduced chemical costs for phosphorus removal and savings in sludge disposal costs, Ohio's detergent phosphorus ban is a pragmatic component of an international phosphorus management strategy to protect the Great Lakes.     

IMPACT OF RIPARIAN FOREST BUFFERS ON AGRICULTURAL NONPOINT SOURCE POLLUTION1

ABSTRACT: A field monitoring study of a riparian forest buffer zone was conducted to determine the impact of the riparian ecosystem on reducing the concentration of agricultural nonpoint source pollutants. Groundwater samples were collected from 20 sampling locations between May 1993 and December 1994, and analyzed for NO₃-N, PO₄, and NH₄-N. Statistical analyses such as Friedman's test, cluster analysis, cross correlation analysis and Duncan's test were performed for the nutrient data. The study showed that the ripanan buffer zone was effective in reducing nitrate concentrations originating from upland agricultural fields. Instream nitrate concentrations were 48 percent less than those measured in the agricultural field. Reductions in concentrations in sampling locations at the wetland edge ranged from 16 to 70 percent. The mean nitrate concentrations in forested hill slope were 45 percent less than concentrations in a well located in an upland agricultural field. Meanwhile, the concentrations of phosphate and ammonia did not follow any specific spatial trend and were generally higher during the summer season for most sampling locations.