African Wildlife & Environment Issue 77 FINAL ISSUE

CONSERVATION

When freshwater and SALTWATERMEET

From an environmental management perspective, we have been forced into disciplinary silos. These are the product of philosophy of the sciences dating back to Rene Descartes and Francis Bacon, upon which Newtonian physics was based. In my view this has led to a situation where we have drilled down to such detail within each discipline, that we end up knowing more and more about less and less. This is certainly the case when we think of ecosystems, which we seem to divide into aquatic and terrestrial.

My interest is in water, as it flows through landscapes and crosses borders imposed by our own human perspective. These are imaginary borders that exist in our minds only, and as a transboundary water specialist I have invested considerable time in exploring the peculiarities that arise when a natural flow of water is intersected by a man-made boundary. Several boundaries exist, all reinforced by our academic structures and disciplinary silos. Three of these are of interest to me – freshwater surface flows including rivers and wetlands, aquifers and their invisible mysteries that dictate how groundwater works, and coastal waters

Prof Anthony Turton

sinks to the bottom, and freshwater is less dense, so it floats over the top. These two bodies of water behave differently and are separated by a clearly defined halocline. Where these two bodies of water meet, we often have different temperatures and sediment loads, so they each manifest as clearly visible colours, often with a thermocline between them. A thermocline separates water of different temperature, so in many cases where freshwater

particularly those around estuaries. In these places all three of these artificially defined systems intersect, so who is the resident expert in each? An ecologist? A hydrologist? A hydrogeologist? A limnologist or an oceanographer? All are specialist fields populated by absolute experts, but the way they intersect has always fascinated me. I have invested considerable time in exploring the interface to the point where I can now present some of my preliminary findings. In Issue 76 of African Wildlife and Environment I presented some work on estuaries, focusing on the fact that freshwater behaves differently to saltwater, because of fundamental physics and chemistry. A brief summary of what I presented in that article is centred

meets saltwater, there is both a halocline and a thermocline, which happen to coincide at that precise point of contact. Whitfield (1999) shows that both temperature and salinity are of importance to the assemblages of marine organisms. Image 1: Groot Brak River estuary and beach at Botha and Outeniqua Strand showing all the key elements of freshwater flows from an aquifer into the ocean. Image courtesy of Google Earth.

on the fact that freshwater is less dense than saltwater, so it flows on top of it where they meet, and mixing is quite difficult. Between these two bodies of water, a halocline exists. That halocline can be thought of as a barrier separating water of different salinities. Saline water is denser, so it

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