Abstract
The hyporheic zone (HZ), as the connecting ecotone between surface- and groundwater, is functionally part of both fluvial and groundwater ecosystems. Its hydrological, chemical, biological and metabolic features are specific of this zone, not belonging truly neither to surface- nor to groundwater. Exchanges of water, nutrients, and organic matter occur in response to variations in discharge and bed topography and porosity. Dynamic gradients exist at all scales and vary temporally. Across all scales, the functional significance of the HZ relates to its activity and connection with the surface stream. The HZ is a relatively rich environment and almost all invertebrate groups have colonized this habitat. This fauna, so-called hyporheos, is composed of species typical from interstitial environment, and also of benthic epigean and phreatic species. The hyporheic microbiocenose consists in bacteria, archaea, protozoa and fungi. The HZ provides several ecosystem services, playing a pivotal role in mediating exchange processes, including both matter and energy, between surface and subterranean ecosystems, functioning as regulator of water flow, benthic invertebrates refuge and place of storage, source and transformation of organic matter. The hyporheic zone is one of the most threatened aquatic environments, being strongly influenced by human activities, and the least protected by legislation worldwide. Its maintenance and conservation is compelling in order to preserve the ecological interconnectivity among the three spatial dimensions of the aquatic environment. Although several researchers addressed the importance of the hyporheic zone early, and most contemporary stream ecosystem models explicitly include it, very little is known about the HZ of Neotropical regions. From a biological standpoint, hyporheos fauna in Neotropical regions are still largely underestimated. This review focuses on a brief presentation of the hyporheic zone and its functions and significance as an ecotone. We also highlighted the key aspects considering also the current status of research in Neotropical regions.
Highlights
The water bodies are a broad integrated system that constitutes the “hydrologic landscape” of a given territory in complex networks of surface water, lakes, wetlands, rivers and groundwater
Groundwater contribution has great importance in composition of surface waters (Hynes, 1983), and surface water depends on base flow (Boulton and Hancock, 2006), that is, the percentage of water in a channel that emerges from the underground
This relationship is due to two factors: i) the water passing through the substrate will, with time, be incorporated into the superficial system, ii) in many rivers, during the dry period, the base flow may constitute the majority of the water flowing in the channel
Summary
The water bodies are a broad integrated system that constitutes the “hydrologic landscape” of a given territory in complex networks of surface water, lakes, wetlands, rivers and groundwater. The interactions and range of hydrological and biogeochemical exchanges between surface water and groundwater are determined by the structure of the basin, reflecting the permeability of the aquifer, the local and regional geology, the water storage capacity of the river plain, the channel morphology, the topographical structure, the hydraulic conductivity of the riverbed sediments, the waterfront and the variations of recharge rate (Dahm et al, 1998; Wroblicky et al, 1998) These interactions influence both key stream ecosystem processes, such as primary productivity and nutrient cycling, and microbe and invertebrate communities’ diversity and spawning from some fish (see Boulton et al, 2010 and references therein). We highlighted the key aspects considering the current status of research in Neotropical regions
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