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Abstract Headwater wetlands are important sites for carbon storage and emissions. While local- and landscape-scale factors are known to influence wetland carbon biogeochemistry, the spatial and temporal heterogeneity of these factors limits our predictive understanding of wetland carbon dynamics. To address this issue, we examined relationships between carbon dioxide (CO₂) and methane (CH₄) concentrations with wetland hydrogeomorphology, water level, and biogeochemical conditions. We sampled water chemistry and dissolved gases (CO₂and CH₄) and monitored continuous water level at 20 wetlands and co-located upland wells in the Delmarva Peninsula, Maryland, every 1–3 months for 2 years. We also obtained wetland hydrogeomorphologic metrics at maximum inundation (area, perimeter, and volume). Wetlands in our study were supersaturated with CO₂(mean = 315 μM) and CH₄(mean = 15 μM), highlighting their potential role as carbon sources to the atmosphere. Spatial and temporal variability in CO₂and CH₄concentrations was high, particularly for CH₄, and both gases were more spatially variable than temporally. We found that groundwater is a potential source of CO₂in wetlands and CO₂decreases with increased water level. In contrast, CH₄concentrations appear to be related to substrate and nutrient availability and to drying patterns over a longer temporal scale. At the landscape scale, wetlands with higher perimeter:area ratios and wetlands with higher height above the nearest drainage had higher CO₂and CH₄concentrations. Understanding the variability of CO₂and CH₄in wetlands, and how these might change with changing environmental conditions and across different wetland types, is critical to understanding the current and future role of wetlands in the global carbon cycle. 

Abstract Globally significant quantities of carbon (C), nitrogen (N), and phosphorus (P) enter freshwater reservoirs each year. These inputs can be buried in sediments, respired, taken up by organisms, emitted to the atmosphere, or exported downstream. While much is known about reservoir-scale biogeochemical processing, less is known about spatial and temporal variability of biogeochemistry within a reservoir along the continuum from inflowing streams to the dam. To address this gap, we examined longitudinal variability in surface water biogeochemistry (C, N, and P) in two small reservoirs throughout a thermally stratified season. We sampled total and dissolved fractions of C, N, and P, as well as chlorophyll-a from each reservoir’s major inflows to the dam. We found that heterogeneity in biogeochemical concentrations was greater over time than space. However, dissolved nutrient and organic carbon concentrations had high site-to-site variability within both reservoirs, potentially as a result of shifting biological activity or environmental conditions. When considering spatially explicit processing, we found that certain locations within the reservoir, most often the stream–reservoir interface, acted as “hotspots” of change in biogeochemical concentrations. Our study suggests that spatially explicit metrics of biogeochemical processing could help constrain the role of reservoirs in C, N, and P cycles in the landscape. Ultimately, our results highlight that biogeochemical heterogeneity in small reservoirs may be more variable over time than space, and that some sites within reservoirs play critically important roles in whole-ecosystem biogeochemical processing. 

Abstract Animal waste can contribute substantially to nutrient cycling and ecosystem productivity in many environments. However, little is known of the biogeochemical impact of animal excretion in wetland habitats.Here we investigate the effects of wood frog (Lithobates sylvaticus) tadpole aggregations on nutrient recycling, microbial metabolism and carbon cycling in geographically isolated wetlands.We used a paired mesocosm and field study approach that utilized measurements of tadpole excretion rates, microbial extracellular enzyme activities, and litter degradation.We found a strong relationship between tadpole development and nutrient excretion, demonstrating that ontological changes impact tadpole‐mediated nutrient cycling in wetland habitats. Further, the interplay between population‐level tadpole excretion and wetland hydrologic conditions increased ambient and concentrations by 56 and 14 times, respectively, compared to adjacent wetlands without tadpoles. Within our mesocosm study, microbes decreased extracellular enzyme production associated with nitrogen acquisition in response to the presence of tadpole‐derived nitrogen. In addition to microbial metabolic responses, tadpole presence enhanced litter breakdown in both mesocosms and wetlands by 7% and 12%, respectively, in comparison to reference conditions.These results provide evidence for the functional and biogeochemical role of tadpole aggregations in wetland habitats, with important implications for ecosystem processes, biodiversity conservation, and ecosystem management.