Sites characterization
The first two PCA axes explained 64.1% of the overall variance (Fig. 2). The first axis (43.5%) illustrated the environmental differences between land uses. Agricultural RWs were characterized by higher nutrient concentration (total phosphorus, total nitrogen, soluble reactive phosphorus, and to a lesser extent, ammonium). By contrast, livestock RWs were characterized by higher values of pH, conductivity, and TDS and lower values of nutrient concentrations (Online Resource: Table S2, correlations between axis and variables). The second axis (20.6% of the total variance) was positively correlated with temperature, nitrate, and nitrite whereas was negatively correlated with flow and dissolved oxygen. This axis showed the difference between hydrological periods in livestock RWs, with respect to temperature, DO and flow. The dry period was characterized by higher temperature, lower flow and DO in comparison with the normal period.
Significant differences were found in water physical and chemical characteristics between land uses (Table 1). Agricultural RWs exhibited higher values of total phosphorus (F1,6 = 34.50 , p = 0.001), total nitrogen (F1,6 = 116.94 ,p < 0.001), and P-PO4 (F1,6 = 44.84 ,p < 0.001). By contrast, livestock RWs had higher values of conductivity (F1,34 = 250.33 , p < 0.001), TDS (F1,34 = 147.72, p < 0.001) and pH (F1,34 = 169.51, p < 0.001) in both hydrological periods. Dissolved oxygen concentration was lower in the dry period in comparison with normal period in RWs of both land uses and also, was lower in agricultural RWs than in livestock RWs in the dry period (F1,34 = 4.480, p = 0.042). In contrast, temperature was higher in the dry period in both land uses (F1,34 = 51.67, p < 0.001). Biochemical oxygen demand showed differences between hydrological periods, with higher values in the dry period, only in agricultural RWs (F1,6 = 16.98, p = 0.006).
Macrophytes
We recorded 15 species during the study, and the total coverage of macrophytes was always greater than 60% in the RWs studied (Table 2). No significant differences were found in richness (estimate = 0.18, zvalue = 0.43, p = 0.670; estimate = 0.29, zvalue = 0.65, p = 0.51), diversity (F1,7 = 0.10, p = 0.763; F1,7 = 1.72, p = 0.231) or total coverage (F1,7 = 0.00, p = 0.956; F1,7 = 0.94, p = 0.346) between land uses and hydrological periods, respectively. Coverage of floating-anchored species was higher in agricultural RWs than in livestock RWs (F1,7 = 637.14, p < 0.001), where coverage of emergent macrophytes was higher (F1,7 = 82.41, p < 0.001). Submerged macrophytes were not recorded in agricultural RWs. Typha latifolia, H. ranunculoides, A. philoxeroides, and L. peploides were the dominant species in the agricultural RWs, whereas I. pseudacorus and S. californicus were the dominant in livestock RWs. Unlike the normal period characterized by a higher coverage of emergent macrophytes (F1,7 = 19.70, p = 0.003), the dry period was characterized by a higher coverage of a free-floating species (L. gibba, F1,7 = 10.73, p = 0.014). With respect to floating-anchored macrophytes they respond differently in each land use, decreasing their coverage in the dry period in agricultural RWs and increasing in that period in livestock ones (Online Resource: Table S3).
Macroinvertebrates
A total of 63 taxa of macroinvertebrates were collected in the RWs studied (Online Resource: Table S4). Taxa richness differed significantly between land uses (estimate = 0.39, zvalue = 2.68, p = 0.007), with an average of 13 taxa in agricultural RWs and an average of 20 taxa in livestock RWs (Fig. 3). Mean density also differed between land uses (F1,37 = 31.26, p < 0.001), with agricultural RWs showing half the density of livestock RWs (Fig. 3). In addition, the density found during the dry period for the two land uses was half that recorded for the normal period (F1,37=34.40, p<0.001, Fig. 3). Diversity only showed significant differences between land uses in the dry period (F1,37 = 5.48, p = 0.025), with higher values in livestock RWs than in agricultural RW (Online Resource: Table S5).
Regarding FFGs, 26 taxa were identified as predators, 23 as collector-gatherers, 7 as scrapers, 5 as collector-filterers, and 2 as shredders (Online Resource: Table S4). Free-living aquatic nematodes were not included in the FFG analysis due to the controversies in the FFG classification (Moens et al. 2006; López van Oosterom et al. 2013). In the comparison between land uses, agricultural RWs showed higher relative abundance of predators (F1, 37 = 5.87, p = 0.020) and scrapers (F1, 37 = 6.15, p = 0.012, Fig. 4). By contrast, livestock RWs exhibited a higher relative abundance of collector-gatherers in both periods (F1, 37 = 6.50, p = 0.015) and a higher relative abundance of collector-filterers in the dry period, coinciding with a reduction of this FFG in the agricultural RWs (significant interaction, F1, 37 = 10.567, p = 0.002; Fig. 4). Differences between hydrological periods were also found: the dry period exhibited higher relative abundance of predators (F1, 37 = 28.63, p < 0.001) than the normal period, which had a significantly higher relative abundance of shredders (F1, 37 = 26.39, p < 0.001, Fig. 4).
The assemblage compositions differed significantly between land uses (PERMANOVA: pseudo-F1,37 = 16.46, P = 0.001) and hydrological periods (PERMANOVA: pseudo-F1,37 = 12.39, P = 0.001). Based on SIMPER analysis results, the dissimilarity between land uses in the normal period was 48%, whereas the dissimilarity increased to 67% in the dry period. The taxa that contributed the most to differences between agriculture and livestock were Hyalella curvispina (Shoemaker, 1942) (5.80%), Oligochaeta (5.33%), Uncancylus concentricus (dOrbigny, 1835) (5.29%), Cyclopoida (5.18%), Cladocera (4.97%), Chironomidae (4.79%), and Caenis sp. (4.64%) (with higher abundance in livestock than agricultural RWs) and Dugesiidae (4.68%) and Entomobrydae (3.47%) with higher abundance in agricultural RWs. The differences between hydrological periods were attributed to the decreased abundance of H. curvispina (7.92% in livestock, 7.48% in agriculture), Dugesiidae (5.29% in livestock, 10.42% in agriculture), and Caenis sp. (4.88% in livestock) in dry periods and the increased abundance of particular taxa such as Nematoda (4.00% in livestock, 4.09% in agriculture), Cyclopoida (3.79% in livestock, 5.73% in agriculture), and Ceratopogonidae (4.43% in livestock).