The objective of this study was to assess the temporal and spatial variability of aquatic invertebrates and microbial parameters (biomass and activity) with environmental data in springs, and to determine the impact of key parameters on the ecological situation of a groundwater system. Eight springs in the two study areas of Baumberge and Schöppinger Berg (W-NW of Münster, North Rhine Westphalia, Germany) were sampled at three sampling campaigns between 2018 and 2019. Physicochemical parameters of the spring samples and abundances of aquatic invertebrates were determined at each sampling event. Samples for hydro(geo)chemical and microbial analyses were collected during each sampling campaign in the springs. Spearman correlation and principal component analysis were used to identify the key parameters. The abundance of aquatic invertebrates and microbial activity were significantly positively correlated with groundwater table fluctuation. The abundance of stygobite individuals was significantly positively correlated with the Groundwater-Fauna-Index and phosphate in Baumberge, and negatively correlated with chloride in Schöppinger Berg. Most notably, the stable isotopes of water and microbial activity were significantly inversely correlated. The hydro(geo)chemical results showed no significant spatial differences in groundwater in both groundwater systems. Stable isotopes of water indicate a meteoric origin, with an effect of evaporation for two months, even though the downward percolation and groundwater recharge rates are high. The nitrate concentration was higher than 50 mg/L only in SB due to the agricultural activities. Nitrate input into groundwater comes from two sources in Baumberge, while it comes from one source in Schöppinger Berg. There was no evidence of denitrification in both areas. Secondary gypsum is assumed to be the source of sulfate in groundwater in Schöppinger Berg, but anaerobic oxidation of pyrite in the deeper part of the groundwater system as a source of sulfate cannot be excluded.
The main aim of this study was to investigate the abundance of invertebrates in groundwater in relation to groundwater conditions (groundwater table, discharge, rainfall, and physio-chemical parameters), and to examine the suitable time for invertebrate sampling in springs. Thus, eight springs in two separate study areas, “Baumberge” and “Schöppinger Berg” (Münsterland area, North-Rhine Westphalia in Germany), were sampled five times (24 h for 2–5 consecutive sampling days) between November 2018 and October 2019. The results showed high spatial and temporal variance. In general, the existence of invertebrates and stygobites increased, whereas invertebrate types decreased with increasing hydraulic head and spring discharge. Therefore, investigating the abundance of invertebrates and invertebrate species is recommended to be done separately. Abundance of invertebrates was affected by different factors in both areas. Spearman correlation test (two-tailed) and factor analyses (n = 80, p ≤ 0.01) highlighted the importance of detritus as the main controlling factor for invertebrate existence and stygobite individuals in Baumberge, whereas dissolved oxygen is essential for their existence in Schöppinger Berg.
ZusammenfassungZwei Untersuchungsgebiete im zentralen Münsterland (Baumberge, NRW, Deutschland) sind aufgrund der geologischen Reliefumkehr-Situation isolierte Grundwasser-Ökosysteme, welche nur von infiltrierendem Niederschlagswasser beeinflusst werden. Als sogenannte „Natur-Lysimeter“ eignen sie sich mit ihren insgesamt bis zu 200 natürlichen Quellaustritten als multidisziplinäre Bezugssysteme für wasserdurchlässige Kluftgrundwasserleitersysteme (aus Kalkmergelsteinen). Die Betrachtung der langjährigen Veränderungen des Stoffaustrags an den Quellen deuten auf zunehmende Verkarstung und raumzeitlich wechselnde Einflüsse durch die land- und forstwirtschaftlich genutzte Geländeoberfläche hin. Stabile Sulfatisotope zeigen, dass die Mehrheit der Quellen durch den Eintrag von Gülle in deren Quell-Einzugsgebiet beeinflusst wird und dass die Pyritoxidation ein wichtiger Prozess im tieferen Grundwasserkörper ist. Die Nitratkonzentrationen sind im Allgemeinen hoch (über 50 mg/l) und stammen aus Gülle und/oder Kunstdünger, wie stabile Nitratisotope zeigen. Der ökologische Zustand des Grundwassersystems wird aufgrund von Crustaceen im Grundwasser als gut bewertet. Der Stoffaustrag jedes noch so kleinen Quellaustritts zeigt mit dem Grundwasserstand sich verändernde Zumischungsanteile von tieferem Grundwasser an.
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