Constraining natural and anthropogenic disturbances in the delivery of coastal ecosystem services

Coastal ecosystems provide key services that benefit human wellbeing yet are undergoing rapid degradation due to natural and anthropogenic pressures. This thesis seeks to understand how disturbances impact salt marsh and estuarine ecosystem functioning in order to refine their role in coastal ecosystem service delivery and predict future resilience. Salt marsh survival relative to sealevel rise increasingly relies on the accumulation and preservation of soil organic carbon (SOC). Firstly, I characterized SOC development and turnover in a New England salt marsh and found that salt marsh soils typically store marsh grass-derived compounds that are reworked over centuries-to-millennia. Next, I assessed how two common marsh disturbances – natural ponding and anthropogenic mosquito ditching – affect salt marsh carbon cycling and storage. Salt marsh ponds deepen through soil erosion and decomposition of long-buried marsh peat. Further, the SOC lost during pond development is not fully recouped once drained ponds are revegetated and virtually indistinguishable from the surrounding marsh. Mosquito ditches, which were installed in ~ 90% of New England salt marshes during the Great Depression, did not significantly alter marsh carbon storage. In Buzzards Bay, Massachusetts, a US National Estuary, we tested relationships among measures of estuarine water quality, recreational activity, and local socioeconomic conditions to understand how the benefits of cultural ecosystem services are affected by shifts in water quality associated with global change and anthropogenic activity. Over a 24-year period, water quality degradation coinciding with increases in Chlorophyll a is associated with declines in fishery abundance and cultural ecosystem service values ($0.08 – 0.67 million USD). In combination, incorporation of both anthropogenic and natural disturbances to coastal ecosystem functioning and service delivery can produce improved estimates of ecosystem service valuation for effective resource decision-making under future climate scenarios.

The effects of defaunation on plants’ capacity to track climate change

Seed dispersal in decline Most plant species depend on animals to disperse their seeds, but this vital function is threatened by the declines in animal populations, limiting the potential for plants to adapt to climate change by shifting their ranges. Using data from more than 400 networks of seed dispersal interactions, Fricke et al . quantified the changes in seed disposal function brought about globally by defaunation. Their analyses indicate that past defaunation has severely reduced long-distance seed dispersal, cutting by more than half the number of seeds dispersed far enough to track climate change. In addition, their approach enables the prediction of seed dispersal interactions using species traits and an estimation of how these interactions translate into ecosystem functioning, thus informing ecological forecasting and the consequences of animal declines. —AMS

Species losses, gains, and changes in persistent species are associated with distinct effects on ecosystem functioning in global grasslands

Global change drivers such as anthropogenic nutrient inputs simultaneously alter biodiversity, species composition, and ecosystem functions such as above ground biomass. These changes are interconnected by complex feedbacks among extinction, invasion, and shifting relative abundance. Here, we use a novel temporal application of the Price equation to separate species richness and biomass change through time and quantify the functional contributions of species that are lost, gained, and persist under ambient and experimental nutrient addition in 59 global grasslands. Under ambient conditions, compositional and biomass turnover was high, but species losses (i.e., local extinctions) were balanced by gains (i.e. colonization). Under fertilization, there was biomass loss associated with species loss. Few species were gained in fertilized conditions over time but those that were, and species that persisted, contributed to net biomass gains, outweighing biomass loss. These components of community change are associated with distinct effects on measures of ecosystem functioning.