African Wildlife & Environment Issue 77 FINAL ISSUE

CONSERVATION

plumes is confirmed by the haloclines indicated in the image. The conclusion we can draw from this study is that freshwater flowing from the land into the ocean moves through two different pathways. The first pathway typically understood is via an estuary, which manifests as a dominant plume clearly defined by sediment load and a halocline. The second pathway is less well described and is via diffuse flows out of a coastal aquifer. These freshwater flows are likely to form a distinct component to the local ecosystem, and ought to be studied in greater detail.The assemblage structure of marine organisms along a stretch of coast adjacent to a free-flowing aquifer is likely to be fundamentally different from that where no aquifer is present. Furthermore, from an Environmental Impact Assessment (EIA) perspective, the abstraction of water from a coastal aquifer is likely to impact the close inshore ocean environment in a way greater than we might currently believe to be the case. To this end it would be useful to document some before and after images where large-scale irrigation, clearly visible as centre pivots, have been authorised by the Department of Water and Sanitation (DWS). These observations should be regarded as tentative until such time as they have been confirmed by independent research. If valid, then future work to identify the presence of persistent freshwater flows from coastal aquifers, and correlation with ichthyofaunal assemblages, would be very useful. FURTHER READING Turton,A.R. 2020. Does Freshwater Flow into the Ocean Constitute aWasted Resource? AfricanWildlife and Environment 76 : 8-10. Whitfield,A.K. 1999. Ichthyofaunal Assemblages in Estuaries:A South African Case Study. Reviews in Fish Biology and Fisheries 9 ; 151 – 186.

surf, which is forced away from the shore by the presence of freshwater on the surface.When the pressure from the freshwater lens floating on the surface equals the pressure of the incoming waves, it forces a pathway through the line of breaking waves, sometimes with such clarity that foam from the breaking waves is also absent. Confirmation that these plumes are indeed freshwater flows is found in the clearly visible sediment plumes and haloclines visible to the satellite. Image 3 was taken on 3 July 2019 and it displays another interesting manifestation. When compared to the same image taken on 21 August 2015 (Image 2), the flows of freshwater from the river estuary confirms the interpretation presented above. Diffuse flows from an aquifer manifest as distinctly 'L' shaped plumes penetrating the surf line, while a free- flowing estuary manifests as a single dominant plume defined by a clearly visible halocline (refer to Turton, 2020). In this case the estuary is closed and the river flow so weak, but not insignificant, that it resembles that of an aquifer rather than an estuary. When focussing on the sub-surface flow of freshwater into the ocean through an alluvial fan so pronounced that it creates a lagoon, we can clearly see from Image 4 , taken on 22 November 2019, that the river flow is insignificant when compared to the diffuse flow from the coastal aquifer. In this case the aquifer flow is clearly visible as pronounced 'L' shaped plumes through the surf line. The presence of the freshwater Image 4: Satellite image taken on 22 November 2019 showing a predominantly aquifer flow with the river closed by sediment and in a low flow condition. Image courtesy of Google Earth.

Prof Anthony Turton Centre for Environmental Management University of the Free State

18 | African Wildlife & Environment | Issue 77 (2020)