Biogeochemical cycling in restored and unrestored coastal wetlands of Lake Ontario

Abstract

Wetlands provide many ecosystem services, including carbon burial and nutrient pollution remediation from excessive anthropogenic inputs. In response to loss and degradation of Laurentian Great Lake coastal wetlands, restoration efforts along the southern shore of Lake Ontario in recent years aimed to improve habitat quality and biodiversity. It is currently unclear if these restorations impacted biogeochemical processes of key nutrients such as nitrogen (N), phosphorus (P), and carbon. To determine if restoration improved nutrient retention from terrestrial inputs and what factors drive dissolved organic matter (DOM) composition, I analyzed water chemistry, watershed land use, and hydrological connectivity of four restored and four unrestored wetlands over the growing season of 2017 under storm and base flows. All wetlands showed nutrient retention abilities with lower N and P concentrations than their tributaries, but unrestored wetlands had significantly higher nutrient loading and reduction. DOM composition was not significantly affected by restoration, but restored wetlands contained higher concentrations of DOM. N was best removed in the spring, and P was best removed in the fall, with some variation across flow condition. DOM concentration was higher during storm flow and DOM character increased in microbial-like components from spring to fall. DOM, N, and P concentrations correlated positively with agricultural land use across wetlands. The control of watershed-scale land use on downstream water quality coupled with unusually wet conditions of 2017 when these wetlands were sampled may explain why small-scale recent habitat restoration did play a more significant role in N, P, and DOM dynamics. Studying biogeochemistry in wetlands under finer spatial and temporal resolutions over longer time periods may contribute information for future restorative efforts and management practices imposed on Great Lakes coastal wetlands to preserve their health and value.