Fresh groundwater discharge to the global ocean: Spatial distribution of solute fluxes and effects

Abstract:

Coastal fresh groundwater discharge to the ocean, either nearshore or submarine (“coastal groundwater discharge”: CGD), can strongly impact coastal ecosystems. Recently, a spatially explicit numerical modeling effort of CGD (Luijendijk et al., 2020) quantified groundwater discharge from 40,082 coastal catchments, as well as its associated solute fluxes and potential impact on coastal ecosystems. Here we present a spatial analysis of these fluxes and impacts.

Globally, while CGD amounts to just 0.6 % of total freshwater and ~2% of global nitrogen input to the oceans, it poses a risk for eutrophication for a significant proportion of the world’s coastal ecosystems. Spatial variability of CGD is very high, with 10% of the global coastline contributing 90% of the discharge. This leads to a CGD-associated eutrophication risk along 13% of the global coastlines. We discuss the spatial distribution of the groundwater discharge and its eutrophication potential along latitudal gradients and between different landforms and coastal ecosystems.

Uncertainty of this global study is high, it uses globally available datasets of slope, climate, and permeability, the latter provides one global average per rock type. Yet, knowing the regions where CGD could be particularly relevant for coastal ecosystems allows prioritizing areas for regional scale assessments of CGD effects that represent conditions at each particular location in more detail.

Reference:

Luijendijk, E., Gleeson, T., Moosdorf, N., 2020. Fresh groundwater discharge insignificant for the world's oceans but important for coastal ecosystems. Nature Communications, 11(1): 1260.