14 research outputs found
Impact of Riparian Grass Filter Strips on Surface-Water Quality
The effectiveness of natural riparian grass filter strips in removing sediment and agricultural chemicals from surface runoff was studied using no-tillage and conventional-tillage erosion plots. Runoff from the tillage plots was directed onto 4.57, 9.14, and 13.72 m (15, 30, and 45 ft.) length filter strips, where the inflow and outflow concentrations and sediment size distributions were measured. Trapping efficiencies for sediment and agricultural chemicals typically ranged near or above 90 percent, mainly because of high infiltration rates. The filters also significantly reduced peak discharge concentrations, which reduced the impact of sediment and agricultural chemicals on receiving surface waters
Variation of organic matter quantity and quality in streams at Critical Zone Observatory watersheds
The quantity and chemical composition of dissolved organic matter (DOM) in surface waters influence ecosystem processes and anthropogenic use of freshwater. However, despite the importance of understanding spatial and temporal patterns in DOM, measures of DOM quality are not routinely included as part of large-scale ecosystem monitoring programs and variations in analytical procedures can introduce artifacts. In this study, we used consistent sampling and analytical methods to meet the objective of defining variability in DOM quantity and quality and other measures of water quality in streamflow issuing from small forested watersheds located within five Critical Zone Observatory sites representing contrasting environmental conditions. Results show distinct separations among sites as a function of water quality constituents. Relationships among rates of atmospheric deposition, water quality conditions, and stream DOM quantity and quality are consistent with the notion that areas with relatively high rates of atmospheric nitrogen and sulfur deposition and high concentrations of divalent cations result in selective transport of DOM derived from microbial sources, including in-stream microbial phototrophs. We suggest that the critical zone as a whole strongly influences the origin, composition, and fate of DOM in streams. This study highlights the value of consistent DOM characterization methods included as part of long-term monitoring programs for improving our understanding of interactions among ecosystem processes as controls on DOM biogeochemistry
A LONG-TERM, WATERSHED-SCALE, EVALUATION OF THE IMPACTS OF ANIMAL WASTE BMPs ON INDICATOR BACTERIA CONCENTRATIONS1
ABSTRACT: Driven by increasing concerns about bacterial pollution from agricultural sources, states such as Virginia have initiated cost sharing programs that encourage the use of animal waste best management practices (BMPs) to control this pollution. Although a few studies have shown that waste management BMPs are effective at the field scale, their effectiveness at the watershed scale and over the long term is unknown. The focus of this research was to evaluate the effectiveness of BMPs in reducing bacterial pollution at the watershed scale and over the long term. To accomplish this goal, a 1,163 ha watershed located in the Piedmont region of Virginia was monitored over a ten-year period. Fecal coliforms (FC) and fecal streptococci (FS) were measured as indicators of bacterial pollution. A pre-BMP versus post-BMP design was adopted. Major BMPs implemented were manure storage facilities, stream fencing, water troughs, and nutrient management. Seasonal Kendall trend analysis revealed a significant decreasing trend during the post-BMP period for FC concentrations at the watershed outlet, but not at the subwatershed level. Implementation of BMPs also resulted in a significant reduction in the geometric mean of FS concentrations. FC concentrations in streamflow at the watershed outlet exceeded the Virginia primary standard 86 and 74 percent of the time during pre-BMP and post-BMP periods, respectively. Corresponding exceedances for the secondary standard were 50 and 41 percent. Violations decreased only slightly during the post-BMP period. The findings of this study suggest that although BMP implementation can be expected to accomplish some improvement in water quality, BMP implementation alone may not ensure compliance with current water quality standards. (KEY TERMS: nonpoint source pollution; watershed management; water quality; bacterial pollution; fecal coliform; fecal streptococcus; BMP.) INTRODUCTION Contamination from bacterial sources has been identified as the third leading cause of pollution in the nation's rivers, after siltation and nutrients (USEPA, 1999). Pollution from bacteria accounts for nearly 79,820 impaired river miles or 12 percent of the total river miles surveyed in the United States (USEPA, 1999). In Virginia, fecal contamination of surface waters is the leading pollution problem, and agriculture has been cited as the largest contributor of this pollutant (USEPA, 1999). Land application of animal wastes and runoff from livestock facilities are the major agricultural practices contributing to bacterial pollution Although several studies and reviews have evaluated bacterial pollution from agricultural land
Influence of relict milldams on riparian sediment biogeochemistry
Purpose: Riparian zones are important modifiers of nutrient flux between terrestrial and aquatic ecosystems. However, dams alter riparian zones—trapping fine-grained, organic matter-rich sediment and creating poorly mixed, low oxygen conditions—thereby affecting sediment biogeochemistry in poorly understood ways. Methods: We characterized the impact of two relict US mid-Atlantic milldams (one from a primarily agricultural watershed and one from a mixed land use/urban watershed) on spatial patterns of bioavailable element concentrations (Mehlich-3 extractable P, K, Ca, Mg, Mn, Zn, Cu, Fe, B, S, and Na) in sediments upstream and downstream of milldams, with depth, and along transects running parallel and perpendicular to the stream. Results: Element concentrations were not clearly correlated with grain size or organic matter content and, although generally higher, were not significantly more concentrated in upstream riparian sediments when similar (shallow, variably saturated) depths were compared. Pronounced differences were observed: upstream of milldams, sediment concentrations of Ca and Mg were highest in variably saturated shallow sediments, while Fe and Mn were highest in deeper, continuously saturated, low-oxygen sediments. Additionally, data was significantly different by milldam site, a result of differences in land-use histories (e.g., road salt and fertilizer application/runoff) and dominant bedrock geology. Conclusion: Overall, results highlight the combined importance of milldams (and associated influences on groundwater hydrology and sediment redox conditions) and external drivers (other land-use legacies and bedrock geology) in influencing spatial patterns of bioavailable elements in riparian sediments
Data from: Animal-mediated organic matter transformation: aquatic insects as a source of microbially bioavailable organic nutrients and energy
1. Animal communities are essential drivers of energy and elemental flow in ecosystems. However, few studies have investigated the functional role of animals as sources of dissolved organic matter (DOM) and the subsequent utilization of that DOM by the microbial community. 2. In a small forested headwater stream, we tested the effects of taxonomy, feeding traits, and body size on the quality and quantity of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) excreted by aquatic insects. In addition, we conducted steady-state solute additions to estimate instream demand for labile C and compared it to the C excreted by invertebrates. 3. Individual excretion rates and excretion composition varied with body size, taxonomy, and feeding guild. The estimated average community excretion rate was 1.31 μg DOC· per mg insect dry weight (DW)-1·h-1 and 0.33 μg DON·mg DW-1·h-1 and individuals excreted DON at nearly twice the rate of 〖"NH" 〗_"4" ^"+" . This DOM was 2-5 times more bioavailable to microbial heterotrophs than ambient stream water DOM. 4. We estimated that the insect community, conservatively, excreted 1.62 mg of bioavailable DOC·m-2·h-1 and through steady-state additions measured an ambient labile C demand as 3.97±0.67 mg C·m-2·h-1. This suggests that insect-mediated transformation and excretion of labile DOC could satisfy a significant fraction (40±7%) of labile C demand in this small stream. 5. Collectively, our results suggest that animal excretion plays an essential functional role in transforming organic matter into microbially bioavailable forms and may satisfy a variable but significant portion of microbial demand for labile C and N
More Than Dirt: Soil Health Needs to Be Emphasized in Stream and Floodplain Restorations
Soil health is not explicitly included in current stream and floodplain restorations. This may be one of the many reasons that stream restorations are not achieving their full restoration and ecological benefits. The lack of design and implementation procedures for providing healthy soils and the absence of specific soil metrics for evaluation are some of the reasons for the non-inclusion of soil health in floodplain restorations. Here, we have brought together a team of researchers and practitioners to provide a blueprint for the inclusion of soil health in floodplain restorations, with a specific emphasis on approaches that may be easily accessible for practitioners. We describe the challenges posed by current restoration procedures for physical, chemical, and biological soil conditions. The top ten soil metrics that could be easily measured and could be leveraged by practitioners to assess floodplain soil conditions before and after restorations were identified and selected. The best design and construction practices for improving soil health on floodplains are presented. We also recommend that the current crediting approaches and regulatory mechanisms for stream restorations be updated to incentivize soil health. The inclusion of soil health will help us attain the ecological services and functional uplift goals that are being targeted by environmental agencies and the restoration community
Stream response to an extreme drought-induced defoliation event
We assessed stream ecosystem-level response to a drought-induced defoliation event by gypsy moth caterpillars (Lymantria dispar) with high-frequency water quality sensors. The defoliation event was compared to the prior year of data. Based on long-term records of precipitation and drought indices, the drought of 2015–2016 in Rhode Island, USA was an extreme climatic event that preceded and likely precipitated the defoliation from insect infestation. Canopy cover in the riparian area was reduced by over 50% increasing light availability which warmed the stream and stimulated autotrophic activity. Frass and leaf detritus contributed particulate carbon and organic nutrients to the stream. Based on locally calibrated s::can spectro::lyser data, nitrate concentration and flux did not significantly increase during defoliation while orthophosphate concentration and flux did significantly increase during part of the defoliation period. Lower mean daily dissolved oxygen (DO) levels and wider diel cycles of DO indicated higher biological activity during the defoliation event. Stream metabolism metrics were also significantly higher during defoliation and pointed to heterotrophic activity dominating in the stream. The increases in stream metabolism were low compared to other studies; in streams with higher nutrient levels (e.g., in agricultural or urban watersheds) the increase in light and temperature could have a stronger influence on stream metabolism. The in-stream metabolic processes and nutrient fluxes observed in response to the drought-driven defoliation event resulted from the long-term deployment of high-frequency water sensors. The proliferation of these water sensors now enable studies that assess ecosystem responses to stochastic, unusual disturbances
Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones
The compounding effects of anthropogenic legacies for environmental pollution are significant, but not well understood. Here, we show that centennial-scale legacies of milldams and decadal-scale legacies of road salt salinization interact in unexpected ways to produce hot spots of nitrogen (N) in riparian zones. Riparian groundwater and stream water concentrations upstream of two mid-Atlantic (Pennsylvania and Delaware) milldams, 2.4 and 4 m tall, were sampled over a 2 year period. Clay and silt-rich legacy sediments with low hydraulic conductivity, stagnant and poorly mixed hydrologic conditions, and persistent hypoxia in riparian sediments upstream of milldams produced a unique biogeochemical gradient with nitrate removal via denitrification at the upland riparian edge and ammonium-N accumulation in near-stream sediments and groundwaters. Riparian groundwater ammonium-N concentrations upstream of the milldams ranged from 0.006 to 30.6 mgN L−1 while soil-bound values were 0.11–456 mg kg−1. We attribute the elevated ammonium concentrations to ammonification with suppression of nitrification and/or dissimilatory nitrate reduction to ammonium (DNRA). Sodium inputs to riparian groundwater (25–1,504 mg L−1) from road salts may further enhance DNRA and ammonium production and displace sorbed soil ammonium-N into groundwaters. This study suggests that legacies of milldams and road salts may undercut the N buffering capacity of riparian zones and need to be considered in riparian buffer assessments, watershed management plans, and dam removal decisions. Given the widespread existence of dams and other barriers and the ubiquitous use of road salt, the potential for this synergistic N pollution is significant
Influence of land use and hydrologic variability on seasonal dissolved organic carbon and nitrate export: insights from a multi-year regional analysis for the northeastern USA
Land use/land cover (LULC) change has significant impacts on nutrient loading to aquatic systems and has been linked to deteriorating water quality globally. While many relationships between LULC and nutrient loading have been identified, characterization of the interaction between LULC, climate (specifically variable hydrologic forcing) and solute export across seasonal and interannual time scales is needed to understand the processes that determine nutrient loading and responses to change. Recent advances in high-frequency water quality sensors provide opportunities to assess these interannual relationships with sufficiently high temporal resolution to capture the unpredictable, short-term storm events that likely drive important export mechanisms for dissolved organic carbon (DOC) and nitrate (NO3−–N). We deployed a network of in situ sensors in forested, agricultural, and urban watersheds across the northeastern United States. Using 2 years of high-frequency sensor data, we provide a regional assessment of how LULC and hydrologic variability affected the timing and magnitude of dissolved organic carbon and nitrate export, and the status of watershed fluxes as either supply or transport controlled. Analysis of annual export dynamics revealed systematic differences in the timing and magnitude of DOC and NO3−–N delivery among different LULC classes, with distinct regional similarities in the timing of DOC and NO3−–N fluxes from forested and urban watersheds. Conversely, export dynamics at agricultural sites appeared to be highly site-specific, likely driven by local agricultural practices and regulations. Furthermore, the magnitude of solute fluxes across watersheds responded strongly to interannual variability in rainfall, suggesting a high degree of hydrologic control over nutrient loading across the region. Thus, there is strong potential for climate-driven changes in regional hydrologic cycles to drive variation in the magnitude of downstream nutrient fluxes, particularly in watersheds where solute supply and/or transport has been modified