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Questions Can cattle grazing help maintain plant diversity in coastal grasslands? What is the relationship between soil extractable nitrogen and plant diversity in sandy and infertile soils? How does cattle grazing affect soil extractable nitrogen and how might this indirectly impact plant diversity via the N–plant diversity relationship? Location Grazed coastal grasslands on Naushon Island, off of Cape Cod, MA, USA. Methods We surveyed summer vegetation from 2014 to 2017 and analyzed soils for extractable nitrogen (N) in two grazed grasslands on Naushon Island. We also set up cattle enclosures and exclosures to manipulate grazing pressure and test how cattle grazing influenced plant diversity (species richness and Shannon's diversity) and extractable NH4+ and NO3−. In the enclosure experiment, cattle were enclosed for up to a week in the mid‐summer of 2014, 2015, and 2016. For the exclosure experiment, we excluded cattle from areas from 2014 to 2017. Results In both the enclosure and exclosure experiments, higher grazing pressure corresponded to less negative change of plant species richness and Shannon's diversity from 2014 to 2017. Total extractable N had a weak positive correlation with plant diversity, but increasing extractable NO3− correlated with decreasing species richness (p = 0.001) and Shannon's diversity (p = 0.009). Neither the cattle enclosures nor exclosures were related to soil extractable N. Conclusions Cattle grazing may help prevent or slow losses of plant diversity that are occurring in many coastal grasslands, including Naushon Island. This effect does not seem to be regulated by cattle deposition of N in the soil or the N–plant diversity relationship. Our results of the N–plant diversity relationship differ from the mainstream understanding, perhaps due to Naushon's sandy and infertile soils.

As a symptom of accelerated sea level rise and historic impacts to tidal hydrology from agricultural and mosquito control activities, coastal marshes in the Northeastern U.S. are experiencing conversion to open water through edge loss, widening and headward erosion of tidal channels, and the formation and expansion of interior ponds. These interior ponds often form in high elevation marsh, confounding the notion applied in predictive modeling that salt marshes convert to open water when elevation falls below a critical surface inundation threshold. The installation of tidal channel extension features, or runnels, is a technique that has been implemented to reduce water levels and permit vegetation reestablishment in drowning coastal marshes, although there are limited data available to recommend its advisability. We report on 5 years of vegetation and hydrologic monitoring of two locations where a total of 600-m of shallow (0.15–0.30-m in diameter and depth) runnels were installed in 2015 and 2016 to enhance drainage, in the Pettaquamscutt River Estuary, in southern Rhode Island, United States. Results from this Before-After Control-Impact (BACI) designed study found that runnel installation successfully promoted plant recolonization, although runnels did not consistently promote increases in high marsh species presence or diversity. Runnels reduced the groundwater table (by 0.07–0.12 m), and at one location, the groundwater table experienced a 2-fold increase in the fraction of the in-channel tidal range that was observed in the marsh water table. We suggest that restoration of tidal hydrology through runnel installation holds promise as a tool to encourage revegetation and extend the lifespan of drowning coastal marshes where interior ponds are expanding. In addition, our study highlights the importance of considering the rising groundwater table as an important factor in marsh drowning due to expanding interior ponds found on the marsh platform.

Quantifying carbon sequestration by tidal wetlands is important for the management of carbon stocks as part of climate change mitigation. This data publication includes a spatial analysis of carbon accumulation rates in Barnegat and Delaware Bay tidal wetlands. One method calculated long-term organic carbon accumulation rates from radioisotope-dated (Cs-137) sediment cores. The second method measured organic carbon density of sediment accumulated above feldspar marker beds. Carbon accumulation rates generated by these two methods were interpolated across emergent wetland areas, using kriging, with uncertainty estimated by leave-one-out cross validation. This spatial analysis revealed greater carbon sequestration within Delaware, compared to Barnegat Bay. Sequestration rates were found to be more variable within Delaware Bay, and rates were greatest in the tidal freshwater area of the upper bay. Dataset: Supplemental Data