Joseph J. Baustian | USGS Science

USGS2018

Using turbidity measurements to estimate total phosphorus and sediment flux in a Great Lakes coastal wetland

Coastal wetlands around the Laurentian Great Lakes in North America have the potential to intercept surface water coming off of the landscape and reduce the amount of nutrients and sediment entering the lakes. However, extensive coastal wetland areas have been isolated behind dikes and thus have limited interaction with nutrient-rich waters that contribute to harmful algal blooms and other water-quality issues. In this study, we developed a method to use high-frequency measurements of discharge and turbidity to estimate sediment and total phosphorus retention in a hydrologically reconnected coastal wetland. We found sediment and total phosphorus retention to be episodic and highly related to fluctuations in water level. Low water levels in Lake Erie in late 2012 resulted in low retention in the wetland, but sediment and total phosphorus retention increased as water levels rose in the first half of 2013. Overall, the reconnected wetland was a sink for both total phosphorus and suspended sediment and locally reduced phosphorus loading rates to Lake Erie. Additional wetland reconnection projects have the potential to further reduce phosphorus and sediment loading rates, which could improve local water quality and ecosystem health.

Ohio↗

USGS2017

Assessing coastal wetland vulnerability to sea-level rise along the northern Gulf of Mexico coast: Gaps and opportunities for developing a coordinated regional sampling network

Coastal wetland responses to sea-level rise are greatly influenced by biogeomorphic processes that affect wetland surface elevation. Small changes in elevation relative to sea level can lead to comparatively large changes in ecosystem structure, function, and stability. The surface elevation table-marker horizon (SET-MH) approach is being used globally to quantify the relative contributions of processes affecting wetland elevation change. Historically, SET-MH measurements have been obtained at local scales to address site-specific research questions. However, in the face of accelerated sea-level rise, there is an increasing need for elevation change network data that can be incorporated into regional ecological models and vulnerability assessments. In particular, there is a need for long-term, high-temporal resolution data that are strategically distributed across ecologically-relevant abiotic gradients. Here, we quantify the distribution of SET-MH stations along the northern Gulf of Mexico coast (USA) across political boundaries (states), wetland habitats, and ecologically-relevant abiotic gradients (i.e., gradients in temperature, precipitation, elevation, and relative sea-level rise). Our analyses identify areas with high SET-MH station densities as well as areas with notable gaps. Salt marshes, intermediate elevations, and colder areas with high rainfall have a high number of stations, while salt flat ecosystems, certain elevation zones, the mangrove-marsh ecotone, and hypersaline coastal areas with low rainfall have fewer stations. Due to rapid rates of wetland loss and relative sea-level rise, the state of Louisiana has the most extensive SET-MH station network in the region, and we provide several recent examples where data from Louisiana’s network have been used to assess and compare wetland vulnerability to sea-level rise. Our findings represent the first attempt to examine spatial gaps in SET-MH coverage across abiotic gradients. Our analyses can be used to transform a broadly disseminated and unplanned collection of SET-MH stations into a coordinated and strategic regional network. This regional network would provide data for predicting and preparing for the responses of coastal wetlands to accelerated sea-level rise and other aspects of global change.

Alabama, Florida, Louisiana, Mississippi, Texas↗