Agricultural impacts on streams near Nitrate Vulnerable Zones: A case study in the Ebro basin, Northern Spain

Abstract

Agricultural intensification during the last century has caused river degradation across Europe. From the wide range of stressors derived from agricultural activities that impact rivers, diffuse agricultural pollution has received most of the attention from managers and scientists. The aim of this study was to determine the main stressors exerted by intensive agriculture on streams around Nitrate Vulnerable Zones (NVZs), which are areas of land that drain into waters polluted by nitrates according to the European Nitrate Directive (91/676/EEC). The study area was located in the NW of La Rioja (Northern Spain), which has some of the highest nitrate concentrations within the Ebro basin. The relationships between 40 environmental variables and the taxonomic and functional characteristics of the macroinvertebrate assemblages (which are useful indicators of water quality) were analyzed in 11 stream reaches differentially affected by upstream agricultural activity. The streams affected by a greater percentage of agricultural land cover in the surrounding catchment had significantly higher nitrate concentrations than the remaining sites. However, hydromorphological alteration (i.e. channel simplification, riparian forest and habitat degradation), which is closely linked to agricultural practices, was the main factor affecting macroinvertebrate assemblages. We suggest that “good agricultural practices” should be implemented in streams affected by NVZs to reverse stream degradation, in concordance with the European Water Framework Directive (WFD).

An ecological perspective for analysing rural depopulation and abandonment

“…This environmental improvement would reach a peak with active conservation and, to a lesser extent, with the frozen landscape alternative, due to its higher remaining activity, compared with the rest (Figure 3e,f). In contrast, intensification is expected to increase pollution in soils and water due to intensive farming (Ladrera et al., 2019), mining (García‐Carmona et al., 2019), recreational resorts and installations for energy production (Heal et al., 2020). In fact, depopulated territories are often sought as sites for the disposal of hazardous products, such as industrial or radioactive wastes (e.g.…”

“…In this alternative, economic revenues become the priority, favouring a broad range of potential activities, as described above. Overall, intensification tends to consume large amounts of resources and land, and often pollutes watersheds, air and soils (Ladrera et al., 2019).…”

Density and diversity of macroinvertebrates in Colombian Andean streams impacted by mining, agriculture and cattle production

“…High concentrations of TS were found in both the Agricultural and Mining streams, reducing the entry of light to the ecosystem and affecting the energy flow of the system, which lowers its productivity levels as a consequence (Vázquez, Aké-Castillo & Favila, 2011). Furthermore, the increase in TS is related to the sedimentation rate (Vásquez Zapata, 2009) and the increase in fine sediment can, in turn, be a more significant stressor to macroinvertebrate assemblages than increased nutrient concentrations, in streams around agricultural areas (Ladrera et al, 2019). Moreover, this variable can affect a different group of AMI, for example, taxa adapted to swim, scrape or shred, species that respire by plastron, gills and also Coleopterans dependent on a bubble or plastron to breath (Hauer & Resh, 1996;Rabeni, Doisy & Zweig, 2005;Ladrera et al, 2019).…”

“…Furthermore, the increase in TS is related to the sedimentation rate (Vásquez Zapata, 2009) and the increase in fine sediment can, in turn, be a more significant stressor to macroinvertebrate assemblages than increased nutrient concentrations, in streams around agricultural areas (Ladrera et al, 2019). Moreover, this variable can affect a different group of AMI, for example, taxa adapted to swim, scrape or shred, species that respire by plastron, gills and also Coleopterans dependent on a bubble or plastron to breath (Hauer & Resh, 1996;Rabeni, Doisy & Zweig, 2005;Ladrera et al, 2019). In contrast, invertebrates living in the mud, burrowers and filter-collectors can be favored because they feed on fine sediment.…”

Peer Review #2 of "Density and diversity of macroinvertebrates in Colombian Andean streams impacted by mining, agriculture and cattle production (v0.1)"

“…Furthermore, the increase in TS is related to the sedimentation rate (Vásquez Zapata, 2009) and the increase in fine sediment can, in turn, be a more significant stressor to macroinvertebrate assemblages than increased nutrient concentrations, in streams around agricultural areas (Ladrera et al, 2019). Moreover, this variable can affect a different group of AMI, for example, taxa adapted to swim, scrape or shred, species that respire by plastron, gills and also Coleopterans dependent on a bubble or plastron to breath (Hauer & Resh, 1996;Rabeni et al, 2005;Ladrera et al, 2019). In contrast, invertebrates living in the mud, burrowers and filter-collectors can be favored because they feed on fine sediment.…”