A quantitative hydrogeomorphic approach to the classification of temporary wetlands in the DoA±ana National Park (SW Spain)

A quantitative hydrogeomorphic approach was applied to an extensive survey of temporary wetlands in the DoA +/- ana National Park (SW Spain) in search for quantitative thresholds for wetland classification. Twenty freshwater ponds on the aeolian sand mantle and 46 sites on silty-clay substrate, located in the southern marshland, were surveyed during the heaviest rainy period so far recorded (October 1995-September 1997). On average, temporary ponds showed higher water depth, longer flooding period, lower conductivity (< 0.5 mS cm(-1)), lower pH (6.7), lower phosphate concentration (0.4 mu M) and a more balanced proportion of Ca2+/Na+ than temporary marshes. During floods, marshland sites exhibited higher water transparency, pH (9.5), alkalinity (3.5 meq l(-1)), conductivity (8.2 mS cm(-1)), phosphate concentration (0.7 mu M), Na+ and Ca2+ concentrations (97.2 and 3.5 meq l(-1), respectively) than ponds. Study sites were significantly segregated (ANOSIM test: R = 0.88, P < 0.01, n = 92) in relation to water depth and conductivity. A conductivity of 1.6 mS cm(-1) is proposed as a threshold between marshland sites and ponds during floods. Marshland sites were further segregated into two groups (ANOSIM test: R = 0.777, P < 0.01, n = 23) according to the Na+/Ca2+ ratio (in meq l(-1)) at a threshold value of 25. An ordination by PCA showed that five variables grouped 81.4% of the total variance in two axes. The first PCA axis (60.7% of variance) separated temporary wetlands into ponds and marshland sites according to variables related to substrate and hydrology (Na+/Ca2+ ratio, conductivity, water depth and flooding period). Other variables (e.g., water transparency, alkalinity, pH, submersed macrophyte biomass, phosphate, nitrate and planktonic chlorophyll concentrations) did not produce a significant segregation between marshland and pond sites during floods. Further discrimination within each wetland type was thus not achieved.