A novel approach to model exposure of coastal-marine ecosystems to riverine flood plumes based on remote sensing techniques

Abstract

Increased loads of land-based pollutants are a major threat to coastal-marine ecosystems. Identifying the affected marine areas and the scale of influence on ecosystems is critical to assess the impacts of degraded water quality and to inform planning for catchment management and marine conservation. Studies using remotely-sensed data have contributed to our understanding of the occurrence and influence of river plumes, and to our ability to assess exposure of marine ecosystems to land-based pollutants. However, refinement of plume modeling techniques is required to improve risk assessments. We developed a novel, complementary, approach to model exposure of coastal-marine ecosystems to land-based pollutants. We used supervised classification of MODIS-Aqua true-color satellite imagery to map the extent of plumes and to qualitatively assess the dispersal of pollutants in plumes. We used the Great Barrier Reef (GBR), the world's largest coral reef system, to test our approach. We combined frequency of plume occurrence with spatially distributed loads (based on a cost-distance function) to create maps of exposure to suspended sediment and dissolved inorganic nitrogen. We then compared annual exposure maps (2007-2011) to assess inter-annual variability in the exposure of coral reefs and seagrass beds to these pollutants. We found this method useful to map plumes and qualitatively assess exposure to land-based pollutants. We observed inter-annual variation in exposure of ecosystems to pollutants in the GBR, stressing the need to incorporate a temporal component into plume exposure/risk models. Our study contributes to our understanding of plume spatial-temporal dynamics of the GBR and offers a method that can also be applied to monitor exposure of coastal-marine ecosystems to plumes and explore their ecological influences.

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

“…nutrients) and suspended material. Many previous studies have focused on the potential negative effects or risks of river outflows to marine ecosystems as a result of transport of land-based pollutants from rivers to oceans (Alvarez-Romero et al 2013;Costanzini et al 2014;Petus et al 2014aPetus et al , 2014bYu et al 2014;Devlin et al 2015;Fernández-Nóvoa et al 2015). However, currently there is limited understanding of how altered, reduced or complete lack of flow of freshwater affects estuarine and open coastal marine systems (Gillanders and Kingsford 2002).…”

Reserves as tools for alleviating impacts of marine disease

“…, respectively [56]. The secondary water type is typically found more distant to river outflows and is characterized by elevated chlorophyll-a concentrations, with TSS concentrations reduced due to sedimentation closer to coastlines.…”

Potential Enhanced Survivorship of Crown of Thorns Starfish Larvae due to Near-Annual Nutrient Enrichment during Secondary Outbreaks on the Central Mid-Shelf of the Great Barrier Reef, Australia

“…These conditions of elevated phytoplankton biomass are seen both visually, and by water type analysis [44,64,65,67] and ascribed water types (right column panels of Figure 3), following the methodology of Devlin et al [44] and Petus et al [69,70].…”

“…Nutrient loading from these rivers has greatly increased with the proliferation of agriculture and associated fertiliser use in the region [61,62]. The period in which CoTS larvae are in the plankton stages, during November to February, coincides with the point at which the Wet Tropics rivers exhibit high discharge levels each year (Figure 2), with high levels of intra-annual variability, and regularly produce phytoplankton blooms on the GBR shelf in this region [42,43,[63][64][65][66][67]. Measurements of high chlorophyll a concentrations during this period represent an extended period of time, in which conditions of high phytoplankton biomass are optimal for CoTS larval development (see also [38,67]).…”

“…Chlorophyll a concentrations measured on the Cairns-Townsville mid-shelf area during major river discharge periods (December to March), are 0.5-3 µg·L −1 at salinities in the range 30-35 [42,64,68]. Water type descriptions [44,65,70] are derived from true colour MODIS imagery, calibrated against the direct measurement of salinity, temperature, particulate and dissolved nutrients, phytoplankton, total suspended solids (TSS), the diffuse attenuation coefficient of photosynthetically active radiation (K d (PAR)), colored dissolved organic matter (CDOM), chlorophyll a, and herbicides [70]. The ranges and mean values of chlorophyll a for the water types are summarized in Table 1, drawn from Devlin et al [44].…”