Effects of Land Use Intensification on Fish Assemblages in Mediterranean Climate Streams

Abstract

Southern Portugal is experiencing a rapid change in land use due to the spread of intensive farming systems, namely olive production systems, which can cause strong negative environmental impacts and affect the ecological integrity of aquatic ecosystems. This study aimed to identify the main environmental disturbances related with olive grove intensification on Mediterraneanclimate streams in southern Portugal, and to evaluate their effects on fish assemblage structure and integrity. Twentysix stream sites within the direct influence of traditional, intensive, and hyper-intensive olive groves were sampled. Human-induced disturbances were analyzed along the olive grove intensity gradient. The integrity of fish assemblages was evaluated by comparison with an independent set of least disturbed reference sites, considering metrics and guilds, based on multivariate analyses. Along the gradient of olive grove intensification, the study observed overall increases in human disturbance variables and physicochemical parameters, especially organic/nutrient enrichment, sediment load, and riparian degradation. Animal load measured the impact of livestock production. This variable showed an opposite pattern, since traditional olive groves are often combined with high livestock production and are used as grazing pasture by the cattle, unlike more intensive olive groves. Stream sites influenced by olive groves were dominated by non-native and tolerant fish species, while reference sites presented higher fish richness, density and were mainly occupied by native and intolerant species. Fish assemblage structure in olive grove sites was significantly different from the reference set, although significant differences between olive grove types were not observed. Bray-Curtis similarities between olive grove sites and references showed a decreasing trend in fish assemblage integrity along the olive grove intensification gradient. Olive production, even in traditional groves, led to multiple in-stream disturbances, whose cumulative effects promoted the loss of biota integrity. The impacts of low intensity traditional olive groves on aquatic ecosystems can be much greater when they are coupled with livestock production. This paper recommends best practices to reduce negative impacts of olive production on streams, contributing to guide policy decision-makers in agricultural and water management.

Fish Functional Traits Correlated with Environmental Variables in a Temperate Biodiversity Hotspot

“…Studies of fish community responses to riparian land use at multiple scales have concluded that other habitat characteristics or catchment scale land use patterns are greater drivers of community structure than riparian land use [52], [54], [78], [79], [80], [81], but it is not known if there is a change in fish functional traits due to land use in the riparian corridors. We analyzed datasets with land use proportions for three riparian corridor widths and found little difference in the explanatory power among them, and similar to previous studies all riparian zone datasets explained less variation than the entire catchment dataset (Fig.…”

How Does an Invasive Cyprinid Benefit from the Hydrological Disturbance of Mediterranean Temporary Streams?

“…The irregularity of the annual precipitation and the increasing water demand resulted in the construction of numerous reservoirs in southern Portuguese river basins, namely in Guadiana (N = 29) and Sado (N = 22) [39]. All these factors are responsible for major changes in aquatic ecosystems, threatening the native fish fauna [38,40].…”

“…Therefore, the principal anthropogenic pressures upon rivers are diffuse agricultural pollution and organic loading, channelization and water abstraction, which have led to significant water scarcity and quality problems, as well as habitat degradation [38]. The irregularity of the annual precipitation and the increasing water demand resulted in the construction of numerous reservoirs in southern Portuguese river basins, namely in Guadiana (N = 29) and Sado (N = 22) [39].…”

Responses of Intermittent Stream Fish Assemblages to Irrigation Development

“…Other variables that could reflect the impact of irrigation development upon instream habitat were, however, not selected in the forward selection procedure although fine substrate classes (sand, silt and mud) increase their importance towards the end of the study, particularly at the sampling reach presenting the largest proportion of irrigated land area (site 6). The conversion of arable steppes into irrigated cultures, such as intensive olive groves, is accompanied by regular control of non-cultivated vegetation, which frequently results in the presence of bare soil throughout the year (Matono et al, 2013). Such conditions tend to favour severe soil erosion during the rainy season, particularly in new olive groves where tree cover is minimal (Díaz et al, 2011).…”