Prioritizing riparian corridors for ecosystem restoration in urbanizing watersheds

Background

Riparian corridors can affect nutrient, organic matter, and sediment transport, all of which shape water quality in streams and connected downstream waters. When functioning riparian corridors remain intact, they provide highly valued water quality ecosystem services. However, in rapidly urbanizing watersheds, riparian corridors are susceptible to development modifications that adversely affect those ecosystem services. Protecting high quality riparian corridors or restoring low quality corridors are widely advocated as watershed level water quality management options for protecting those ecosystem services. The two approaches, protection or restoration, should be viewed as complementary by watershed managers and provide a foundation for targeting highly functioning riparian corridors for protection or for identifying poorly functioning corridors for restoration. Ascertaining which strategy to use is often motivated by a specific ecosystem service, for example water quality, upon which watershed management is focused. We have previously reported on a spatially explicit model that focused on identifying riparian corridors that have specific characteristics that make them well suited for purposes of preservation and protection focused on water quality. Here we hypothesize that focusing on restoration, rather than protection, can be the basis for developing a watershed level strategy for improving water quality in urbanizing watersheds.

Methods

The model described here represents a geographic information system (GIS) based approach that utilizes riparian characteristics extracted from 40-meter wide corridors centered on streams and rivers. The model focuses on drinking water reservoir watersheds that can be analyzed at the sub-watershed level. Sub-watershed riparian data (vegetation, soil erodibility and surface slope) are scaled and weighted based on watershed management theories for water quality, and riparian restoration scores are assigned. Those scores are used to rank order riparian zones –the lower the score the higher the priority for riparian restoration.

Results

The model was applied to 90 sub-watersheds in the watershed of an important drinking water reservoir in north central Texas, USA. Results from this study area suggest that corridor scores were found to be most correlated to the amount of: forested vegetation, residential land use, soils in the highest erodibility class, and highest surface slope (r² = 0.92, p < 0.0001). Scores allow watershed managers to rapidly focus on riparian corridors most in need of restoration. A beneficial feature of the model is that it also allows investigation of multiple scenarios of restoration strategies (e.g.,  revegetation, soil stabilization, flood plain leveling), giving watershed managers a tool to compare and contrast watershed level management plans.

Spatially explicit modeling of global tidal marsh accumulated carbon storage revealed its heterogeneous evolutionary patterns across world regions during 2001-2020

Tidal marsh ecosystems play a critical role in mitigating global climate change and achieving carbon-neutral targets. Yet, intensifying anthropogenic activities have led to significant losses in tidal marsh areas, which have substantially undermined their carbon sequestration potential. To comprehensively assess the carbon sequestration capacity of tidal marsh ecosystems and inform effective protection and restoration strategies, this study conducted spatially explicit modeling of global tidal marsh accumulated carbon storage at a 1 km resolution from 2001 to 2020 and analyzed their spatiotemporal evolutionary patterns at both global and regional scales. Results indicated that: (1) Global tidal marsh accumulated carbon storage increased from 2.89 Pg to 5.87 Pg between 2001 and 2020, with the United States, Canada, and Russia collectively accounting for 74% of the total; (2) Hotspot analysis revealed a spatial polarization of accumulated carbon storage; (3) Tidal marsh carbon accumulation rates showed substantial heterogeneity across climate zones, averaging 15.8 t C ha-1 yr-1 globally, with CAR in tropical regions significantly exceeding those in temperate and boreal zones. These findings and the 1-km accumulated carbon storage dataset developed in this study provide valuable insights for identifying ecologically vulnerable regions worldwide and evaluating the effectiveness of tidal marsh restoration initiatives, which are supportive of promoting the sustainable management of tidal marsh ecosystems.