Dataset Information

Context is Everything: Interacting Inputs and Landscape Characteristics Control Stream Nitrogen.

ABSTRACT: To understand the environmental and anthropogenic drivers of stream nitrogen (N) concentrations across the conterminous US, we combined summer low-flow data from 4997 streams with watershed information across three survey periods (2000-2014) of the US EPA's National Rivers and Streams Assessment. Watershed N inputs explained 51% of the variation in log-transformed stream total N (TN) concentrations. Both N source and input rates influenced stream NO₃/TN ratios and N concentrations. Streams dominated by oxidized N forms (NO₃/TN ratio > 0.50) were more strongly responsive to the N input rate compared to streams dominated by other N forms. NO₃ proportional contribution increased with N inputs, supporting N saturation-enhanced NO₃ export to aquatic ecosystems. By combining information about N inputs with climatic and landscape factors, random forest models of stream N concentrations explained 70, 58, and 60% of the spatial variation in stream concentrations of TN, dissolved inorganic N, and total organic N, respectively. The strength and direction of relationships between watershed drivers and stream N concentrations and forms varied with N input intensity. Model results for high N input watersheds not only indicated potential contributions from contaminated groundwater to high stream N concentrations but also the mitigating role of wetlands.

SUBMITTER: Jiajia Lin

PROVIDER: S-EPMC8673309 | biostudies-literature | 2021 Jun

REPOSITORIES: biostudies-literature

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Context is Everything: Interacting Inputs and Landscape Characteristics Control Stream Nitrogen.

Jiajia Lin Compton Jana E JE Hill Ryan A RA Herlihy Alan T AT Sabo Robert D RD Brooks J Renée JR Weber Marc M Pickard Brian B Paulsen Steve G SG Stoddard John L JL

Environmental science & technology 20210601 12

To understand the environmental and anthropogenic drivers of stream nitrogen (N) concentrations across the conterminous US, we combined summer low-flow data from 4997 streams with watershed information across three survey periods (2000-2014) of the US EPA's National Rivers and Streams Assessment. Watershed N inputs explained 51% of the variation in log-transformed stream total N (TN) concentrations. Both N source and input rates influenced stream NO<sub>3</sub>/TN ratios and N concentrations. St ...[more]

PMID: 34060819

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Project description:Organic farming, a low intensity system, may offer benefits for a range of taxa, but what affects the extent of those benefits is imperfectly understood. We explored the effects of organic farming and landscape on the activity density and species density of spiders and carabid beetles, using a large sample of paired organic and conventional farms in the UK. Spider activity density and species density were influenced by both farming system and surrounding landscape. Hunting spiders, which tend to have lower dispersal capabilities, had higher activity density, and more species were captured, on organic compared to conventional farms. There was also evidence for an interaction, as the farming system effect was particularly marked in the cropped area before harvest and was more pronounced in complex landscapes (those with little arable land). There was no evidence for any effect of farming system or landscape on web-building spiders (which include the linyphiids, many of which have high dispersal capabilities). For carabid beetles, the farming system effects were inconsistent. Before harvest, higher activity densities were observed in the crops on organic farms compared with conventional farms. After harvest, no difference was detected in the cropped area, but more carabids were captured on conventional compared to organic boundaries. Carabids were more species-dense in complex landscapes, and farming system did not affect this. There was little evidence that non-cropped habitat differences explained the farming system effects for either spiders or carabid beetles. For spiders, the farming system effects in the cropped area were probably largely attributable to differences in crop management; reduced inputs of pesticides (herbicides and insecticides) and fertilisers are possible influences, and there was some evidence for an effect of non-crop plant species richness on hunting spider activity density. The benefits of organic farming may be greatest for taxa with lower dispersal abilities generally. The evidence for interactions among landscape and farming system in their effects on spiders highlights the importance of developing strategies for managing farmland at the landscape-scale for most effective conservation of biodiversity.

Dataset Information

Context is Everything: Interacting Inputs and Landscape Characteristics Control Stream Nitrogen.

Publications

Context is Everything: Interacting Inputs and Landscape Characteristics Control Stream Nitrogen.

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