Valutazione della qualità ambientale della sorgente carsica Su Gologone (Sardegna centro-orientale) mediante l’impiego delle diatomee epilitiche: primi risultati

We report the rst results of a survey carried out in the smaller water emergence of karst spring system Su Gologone (Sardinia) to acquire knowledge on the physico-chemical characteristics of water, the species composition of epilithic diatom community and the applicability of some diatom indices. The environmental quality of the spring was evaluated using the EPI-D index (general biological quality), the NNS and NNS’’ indices (physical disturbance). The results were integrated with the annual dataset of physico-chemical and microbiological variables (Escherichia coli, fecal and total coliforms) and the LIM and LIMeco indices. The results of EPI-D were also compared with those of the IPS (general biological quality), and TI (trophic level) indices. The diatom community was composed by a total of 89 taxa (36 genera), including 25 taxa observed in lotic waters of Sardinia for the rst time. The taxa found in the counts were 39 (21 genera) and those dominant are alkaliphilous, halophobous-oligohalobous tolerant, xenosaprobic--mesosaprobic and characteristic of oligotrophic waters. The EPI-D indicated an excellent-good quality (I-II class) and it seems in good agreement with the environmental variables and with the LIM (good quality: II class) and IPS indices (excellent and good quality: I and II class). By contrast the TI index has decidedly overestimated the trophic state. The NNS and NNS’’ revealed a low degree of physical disturbance, consistent with the low content of suspended solids. The spring showed a slight deterioration of environmental quality in late spring, probably linked to the reduction of discharge and the increased presence of tourists.