Hindcasting Ecosystem Functioning Change in an Anthropogenized Estuary: Implications for an Era of Global Change

Xiaoyu Fang,Antony Knights,Tom Moens,Karline Soetaert,Sven Smolders,Carl Van Colen,Francesco Cozzoli

doi:10.3389/fmars.2021.747833

Abstract

Understanding how altered hydrodynamics related to climate change and anthropogenic modifications affect ecosystem integrity of shallow coastal soft-sediment environments requires a sound integration of how species populations influence ecosystem functioning across heterogeneous spatial scales. Here, we hindcasted how intertidal habitat loss and altered hydrodynamic regimes between 1955 and 2010 associated with geomorphological change to accommodate expansion in anthropogenic activities in the Western Scheldt altered spatial patterns and basin-wide estimates of ecosystem functioning. To this end we combined an empirically derived metabolic model for the effect of the common ragworm Hediste diversicolor on sediment biogeochemistry (measured as sediment oxygen uptake) with a hydrodynamic and population biomass distribution model. Our integrative modeling approach predicted an overall decrease by 304 tons in ragworm biomass between 1955 and 2010, accounting for a reduction by 28% in stimulated sediment oxygen uptake at the landscape scale. Local gains or losses in habitat suitability and ecosystem functioning were primarily driven by changes in maximal current velocities and inundation regimes resulting from deepening, dredging and disposal practices. By looking into the past, we have demonstrated how hydro- and morphodynamic changes affect soft-sediment ecology and highlight the applicability of the integrative framework to upscale anticipated population effects on ecosystem functioning.

Highlights

Coastal ecosystems are at the frontline of environmental change
Using laboratory experiments to characterize ecosystemfunctioning under various natural biomasses, we previously demonstrated that stimulatory ragworm bioturbation effect on sediment oxygen uptake varies proportionally with population biomass in sandy and muddy sediments of tidal flat in the lower region of the estuary (Fang et al, 2021)
This uniformity likely results from the fact that burrow ventilation by ragworms is restricted to the lumen and a few mm in the burrow wall (Nielsen et al, 2004) and suggests that the ragworm bioturbation effect on sediment ecosystem functioning is proportional to its energetic requirements corroborating the allometric scaling exponent of ∼0.75 for the relation between body size and metabolism that is evidenced across taxonomic groups (Brown et al, 2004)

Summary

Introduction

Coastal ecosystems are at the frontline of environmental change. Expanding human activities, accelerating sea level rise, and changing wind climates modify hydrodynamic patterns that define the delicate balance in physical exchange processes that underpin the ecology of these shallow ecosystems (Birchenough et al, 2015; Khojasteh et al, 2021). Soft-sediment dwelling animals (further referred to as macrobenthos, typically including crustaceans, bivalves, and bristle worms) play pivotal roles in the biogeochemical cycling of estuaries and coastal ecosystems by channeling nutrients and carbon assimilated into their biomass to higher trophic levels such as wading birds and fish. These burrowing animals alter biogeochemistry at the sediment-water interface via respiration, excretion, and indirectly through their sediment reworking and ventilation activities (i.e., bioturbation; Kristensen et al, 2012) that importantly stimulate the microbial mineralization of sedimentary organic matter (Snelgrove et al, 2018)

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Results

Conclusion