Greenhouse gas dynamics in shallow aquatic ecosystems in response to a pulse nutrient addition
Abstract
The frequency and severity of storm events is predicted to increase, altering the magnitude and timing of nutrient loading to surface water bodies. These impacts are particularly severe in regions such as the U.S. Midwest, that have a high density of agricultural production and surface water availability. Greenhouse gas (GHG) dynamics in freshwater ecosystems are controlled by variables such as temperature, dissolved oxygen, and nutrient availability, but it is unclear how increasing pulses of nitrogen and phosphorus loading will affect GHG dynamics in shallow aquatic ecosystems. We hypothesized that a pulse addition of nutrients would stimulate aerobic decomposition of autochthonous organic matter, decreasing oxygen availability at the sediment-water interface, leading to increased CH4 flux and decreased N2O flux. To test this, we experimentally pulsed three shallow ponds dominated by submerged macrophytes with additions of nitrogen and phosphorus, paired with three non-pulsed reference ponds, during summer 2020. We measured the response of dissolved CH4 and N2O concentrations, ebullition, methanogenesis potential and denitrification enzyme activity to the experimental nutrient pulses, in addition to other limnological covariates such as dissolved organic carbon and chlorophyll concentration. Prior to the nutrient pulses, GHG dynamics were temporally variable, but concentrations were similar among the manipulated and reference ponds. The nutrient pulses resulted in large increases in CH4 concentrations but minimal change in N2O relative to reference ponds. Strongly reducing conditions likely led to minimized N2O production and the dominance of CH4 as the primary contributor to global warming potential in these shallow systems. Most importantly, the temporal variability in CH4 concentrations and methanogenesis potential increased above baseline variability following the nutrient pulse. Our results suggest that as climate change alters the timing and magnitude of nutrient loading, GHG dynamics in shallow aquatic ecosystems will become more variable.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH114.0005J
- Keywords:
-
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0458 Limnology;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 1807 Climate impacts;
- HYDROLOGY