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Abstract Seagrasses are increasingly recognized for their ecosystem functions and services. However, both natural and anthropogenic stressors impact seagrass functional traits, for example by altering nutrient regimes. Here, we synthesize 27 yr of data from regional, long‐term seagrass and water quality monitoring programs of south Florida to investigate the impacts of relative nutrient availability on seagrass abundance (as expressed by percent cover) across an oligotrophic seascape. We employ linear mixed‐effect models and generalized additive models to show that seagrass abundance is driven by interannual variations in nutrient concentrations, which are ultimately controlled by climate oscillations (El Niño Southern Oscillation Atlantic Multidecadal Oscillation) via regional rainfall‐runoff relationships. Our study suggests that climate oscillations drive interannual variations in seagrass cover on a regional scale, with high‐rainfall years leading to increased nitrogen availability and higher seagrass abundance in typically nitrogen‐limited backreef meadows. Conversely, these periods are associated with reduced seagrass cover at the more P‐limited inshore sites and in Florida Bay, with yet unknown consequences for the provision of seagrass ecosystem services. We show that nutrient delivery from runoff can have diverging impacts on benthic communities, depending on spatial patterns of relative nutrient limitation, with some N‐limited seagrass meadows showing resilience to periodic nutrient enrichment. 

Abstract Direct measurement of methane emissions is cost-prohibitive for greenhouse gas offset projects, necessitating the development of alternative accounting methods such as proxies. Salinity is a useful proxy for tidal marsh CH₄emissions when comparing across a wide range of salinity regimes but does not adequately explain variation in brackish and freshwater regimes, where variation in emissions is large. We sought to improve upon the salinity proxy in a marsh complex on Deal Island Peninsula, Maryland, USA by comparing emissions from four strata differing in hydrology and plant community composition. Mean CH₄chamber-collected emissions measured as mg CH₄m⁻² h⁻¹ranked asS. alterniflora(1.2 ± 0.3) ≫ High-elevationJ. roemerianus(0.4 ± 0.06) > Low-elevationJ. roemerianus(0.3 ± 0.07) = S. patens(0.1 ± 0.01). Sulfate depletion generally reflected the same pattern with significantly greater depletion in theS. alterniflorastratum (61 ± 4%) than in theS. patensstratum (1 ± 9%) with theJ. roemerianusstrata falling in between. We attribute the high CH₄emissions in theS. alterniflorastratum to sulfate depletion likely driven by limited connectivity to tidal waters. Low CH₄emissions in theS. patensstratum are attributed to lower water levels, higher levels of ferric iron, and shallow rooting depth. Moderate CH₄emissions from theJ. roemerianusstrata were likely due to plant traits that favor CH₄oxidation over CH₄production. Hydrology and plant community composition have significant potential as proxies to estimate CH₄emissions at the site scale.