Effect of UVR on lake water and macrophyte leachates in shallow Andean lakes: optical features, nutrient availability and bacteria activity

BASTIDAS NAVARRO M.; E. BALSEIRO; B. MODENUTTI

Punta del Este

Congreso; Shallow Lake Conference; 2008

In shallow lakes with a well developed littoral zone, macrophytes could be a substantial source of dissolved organic matter (DOM). Macrophytes generate DOM either through extracellular release or following aging and subsequent release of dissolved and particulate constituents to the surrounding water. Thus, in shallow lakes this DOM source may be important for bacteria in the carbon cycling. The interaction of DOM and ultraviolet radiation (UVR) results in a progressive loss of colour, decrease spectrophotometric absorbance and lower average molecular size. Molecular weight and size was indicated as an important issue influencing the microbial utilization of DOM, therefore photoalteration caused by short-wavelength solar radiation can be an important factor driving resource bioavailability for bacteria growth. In the present study, we evaluated the effect of UVR exposure on macrophyte leachates and lake water from two Andean shallow lakes, analyzing changes on: 1- optical features of DOM; 2- Soluble Reactive Phosphorous (SRP) and 3- bacteria abundance, activity, and assemblage composition.The study was carried out in two shallow lakes of the Northern Patagonia (Argentina): Lakes Escondido and El Trébol, both lakes are colonized by Scirpus californicus and Potamogenton linguatus. We conducted laboratory experiments in which lake water and macrophytes leachates were exposed or protected to UVR (UVA-340 Q-Panel) in quartz tubes or aluminium foil wrapped. After the exposition we carried out spectrophotometric scans and SRP determination. Finally we performed another experiment in order to analyse bacteria response to leachate addition and UVR-DOM interaction. Thelake water and macrophyte leachates changed their optical features when exposed to UVR. In both cases, the slope of the absorbance curve in the UV region of the spectrum (250-400 nm) was increased after the exposure and the absorbance at short wavelength (