Natural Processes Versus Human Impacts During the Last Century: A Case Study of the Aliakmon River Delta

The Aliakmon River flows down from the northwestern mountains of Greece and is one of the largest fluvial systems in the Greek territory. Basin climate and geology favour the high rates of sediment production and transport and, consequently, the formation of an extensive (9.2% of basin area) bird-foot Holocene delta. Three phases (A, B and C) of human impacts over the past 90 years have caused pronounced changes on the natural evolution of the delta. During Phases A and B, a 50% increase of deltaic sedimentation rates in relation to Holocene pre-anthropogenic rates and an enrichment of deltaic deposits with heavy minerals occurred. Phase C, characterised by damming, increasing agricultural and industrial activities and population growth, resulted in 90% decrease in sedimentation rates compared to Phase B, a regulated hydrological regime with high electrical conductivity and nutrient concentrations of surface water, enhanced erosion of river channel and deltaic deposits and degradation of habitats along the lower Aliakmon River delta. Future climate scenarios and increasing environmental pressures are not compatible with current water use strategy and, given the vulnerability of the system (reservoirs and delta) to projected climate trends, stress for a new strategic natural resource management plan.