Modelling lake metabolism: don’t forget catchment factors

Posted on September 23, 2013

Lakes vary widely in terms of their ability to sustain living (metabolic) processes.  We know that the key metabolic processes of gross primary production (GPP) and respiration (R ) are driven by physical and chemical conditions in lakes – in particular, light penetration, temperature, physical mixing, nutrients and organic matter.  At the same time, these internal lake conditions are strongly affected by background factors associated with lake size, hydrology, catchment size, catchment land use and local geology.   What’s been missing is an evaluation of the relative influence of the direct internal drivers and the indirect, broader-scale factors on lake metabolism.  To fill this knowledge gap, data on water quality, lakemorphometry and catchment conditions were collected from 25 Danish water bodies ranging in size from 0.1 to over 1700 ha in area.  Multiple regression analysis showed that the best single predictor of gross primary production was chlorophyll biomass, which explained 47% of the variation in GPP.  However, predictive power increased to 57% when lake size (mean water depth) was added as a second factor.  In a similar way, dissolved organic carbon explained 52% of the variation in lake respiration, but this rose to 63% when lake size was added to the regression.  And although net lake production (GPP – R) was best predicted by dissolved organic carbon alone (38%), a similar amount  of variation (39%) was predicted by two indirect variables in combination: lake size and the amount of forest cover in the catchment.   In line with its positive correlations with water clarity and mixing depth, and its inverse relationship with nutrient and carbon concentrations, lake size had a negative impact on gross production and respiration.   In contrast, forest cover had a positive impact on net production because of its connection with the input of organic carbon.  Therefore, in making broadscale comparisons of lakes, especially in relation to their responses to human impacts such as nutrient enrichment, deforestation and climate change, there are advantages to be gained by taking into account landscape-level features as well as the physical and chemical factors within the lake.

Reference:   Staehr, P.A., Baastrup-Spohr, L., Sand-Jensen, K. & Stedmon, C.   2012.   Lake metabolism scales with lake morphometry and catchment conditions.  Aquatic  Sciences 74, 155–169.