Selenium Bioaccumulation Across Trophic Levels and Along a Longitudinal Gradient in Headwater Streams.

Toxic effects of selenium (Se) contamination in freshwaters have been well documented. However, study of Se contamination has focused on lentic and larger order lotic systems, whereas headwater streams have received little scrutiny. In central Appalachia, surface coal mining is a common Se source to headwater streams, thus providing a useful system to investigate Se bioaccumulation in headwater food chains and possible longitudinal patterns in Se concentrations. Toward that end, we assessed Se bioaccumulation in 2 reference and 4 mining-influenced headwater streams. At each stream, we sampled ecosystem media, including streamwater, particulate matter (sediment, biofilm, leaf detritus), benthic macroinvertebrates, salamanders, and fish, every 400 m along 1.2- and 1.6-km reaches. We compared media Se concentrations within and among streams and evaluated longitudinal trends in media Se concentrations. Selenium concentrations in sampled media were higher in mining-influenced streams compared with reference streams. We found the highest Se concentrations in benthic macroinvertebrates; however, salamanders and fish bioaccumulated Se to potentially harmful levels in mining-influenced streams. Only one stream demonstrated dilution of streamwater Se with distance downstream, and few longitudinal patterns in Se bioaccumulation occurred along our study reaches. Collectively, our results provide a field-based assessment of Se bioaccumulation in headwater food chains, from streamwater to fish, and highlight the need for future assessments of Se effects in headwater streams and receiving downstream waters. Environ Toxicol Chem 2020;39:692-704. © 2020 SETAC.

Selenium dynamics in headwater streams of the central Appalachian coalfield.

Coal mining can cause selenium (Se) contamination in US Appalachian streams, but linkages between water-column Se concentrations and Se bioaccumulation within Appalachian headwater streams have rarely been quantified. Using elevated specific conductance (SC) in stream water as an indicator of mining influence, we evaluated relationships between SC and Se concentrations in macroinvertebrates and examined dynamics of Se bioaccumulation in headwater streams. Twenty-three Appalachian streams were categorized into 3 stream types based on SC measurements: 1) reference streams with no coal-mining history; 2) mining-influenced, high-SC streams; and 3) mining-influenced, low-SC streams. Selenium concentrations in macroinvertebrates exhibited strong positive associations with both SC and dissolved Se concentrations in stream water. At 3 streams of each type, we further collected water, particulate matter (sediment, biofilm, leaf detritus), and macroinvertebrates and analyzed them for Se during 2 seasons. Enrichment, trophic transfer, and bioaccumulation factors were calculated and compared among stream types. Particulate matter and macroinvertebrates in mining-influenced streams accumulated high Se concentrations relative to reference streams. Concentrations were found at levels indicating Se to be a potential environmental stressor to aquatic life. Most Se enrichment, trophic transfer, and bioaccumulation factors were independent of season. Enrichment factors for biofilm and sediments and bioaccumulation factors for macroinvertebrate predators varied negatively with water-column Se. Our results increase scientific understanding of Se bioaccumulation processes in Appalachian headwater streams. Environ Toxicol Chem 2018;37:2714-2726. © 2018 SETAC.

Spatial and temporal patterns of dissolved nitrogen and phosphorus in surface waters of a multi-land use basin.

Research on relationships between dissolved nutrients and land-use at the watershed scale is a high priority for protecting surface water quality. We measured dissolved nitrogen (DN) and ortho-phosphorus (P) along 130 km of the Calapooia River (Oregon, USA) and 44 of its sub-basins for 3 years to test for associations with land-use. Nutrient concentrations were analyzed for spatial and seasonal patterns and for relationships with land-use and stream discharge. Ortho-P and DN were higher in lower-elevation sub-basins dominated by poorly drained soils and agricultural production compared with higher-elevation sub-basins dominated by well-drained soils and forests. Eight lower basins had at least one sample period with nitrate-N > 10 mg L(-1). The Calapooia River had lower concentrations of dissolved nutrients compared with lower sub-basins, often by an order of magnitude. Dissolved organic N represented a greater proportion of DN in the upper forested sub-basins. Seasonal nutrient concentrations had strong positive correlations to the percent of a sub-basin that was managed for agriculture in all seasons (p values ≤ 0.019) except summer. Results suggest that agricultural lands are contributing to stream nutrient concentrations. However, poorly drained soils in agricultural areas may also contribute to the strong relationships that we found between dissolved nutrients and agriculture.

Poultry litter application to loblolly pine forests: growth and nutrient containment.

Forestland application of poultry manure offers an alternative to the conventional practice of pastureland application. Before such a practice is considered viable, however, it must be demonstrated that the forest ecosystem is capable of absorbing the nutrients contained in poultry manure, especially nitrogen (N) and phosphorus (P). From the forestry perspective, it must also be demonstrated that tree growth is not diminished. We investigated these questions using loblolly pine (Pinus taeda L.) stands growing in central Mississippi in an area of high poultry production. Stockpiled broiler litter was applied to newly thinned, 8-yr-old stands at 0, 4.6, and 18.6 dry Mg ha-1, supplying 0, 200, and 800 kg N ha-1 and 0, 92, and 370 kg P ha-1, respectively. Levels of nitrate in soil water, monitored at a 50-cm depth with porous cup tension lysimeters, exceeded 10 mg N L-1 during the first two years after application in the 18.6 Mg ha-1 rate but only on two occasions in the first year for the lower rate of application. Phosphate was largely absent from lysimeter water in all treatments. Other macronutrients (K, Ca, Mg, S) were elevated in lysimeter water in proportion to litter application rates. Soil extractable nitrate showed similar trends to lysimeter water, with substantial elevation during the first year following application for the 18.6 Mg ha-1 rate. Mehlich III-extractable phosphate peaked in excess of 100 microg P g-1 soil during the third year of the study for the 18.6 Mg ha-1 rate. The 4.6 Mg ha-1 rate did not affect extractable soil P. Tree growth was increased by the poultry litter. Total stem cross-sectional area, or basal area, was approximately 20% greater after 2 yr for both rates of litter application. Overall, the nutrients supplied by the 4.6 Mg ha-1 rate were contained by the pine forest and resulted in favorable increases in tree growth. The higher rate, by contrast, did pose some risk to water quality through the mobilization of nitrate. These results show that, under the conditions of this study, application of poultry litter at moderate rates of approximately 5 Mg ha-1 to young stands of loblolly pine offers an alternative disposal option with minimal impacts to water quality and potential increases in tree growth.