A Spatially Nested Analysis of Land Use Effects on Nutrient Limitation: C and N Interact to Control Autotrophic and Heterotrophic Responses

TL;DRAbstract

Land-use change can alter the spatial variance of carbon, nitrogen and phosphorus (C, N, P) delivery across a watershed and lead to altered nutrient limitation and export patterns. We tested the effects of land-use on C, N, and P limitation in 13 tributary and 3 mainstem locations in the Portneuf River watershed, Idaho using nutrient diffusing substrates. Impacted and nonimpacted sites were paired based on sub-basin size, impact type (minimal, agro-urban), location within the watershed, and discharge. Across all sites, regardless of impact, mean chlorophyll a was significantly stimulated (p < 0.002) by N and N+P addition and suppressed (p< 0.000) by C addition. Ash free dry mass (AFDM) had varying responses to treatment. Chlorophyll a response ratios (treatment/control) were 20% lower for impacted than nonimpacted sites. Autotrophic index (AFDM/chlorophyll a) was significantly lower for N additions and significantly higher for C additions across all sites, suggesting that nutrient addi

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