Comparable Hydrologic Dynamics of Wetlands with and without Persistent Surface Water Connections

A simulation model of hydrology and nutrient dynamics in wetlands

Hydrological and landscape dynamics of floodplain wetlands of the Diara region, Eastern India

<p>Pesticides from agricultural origin may harm surface water quality and pose a risk for aquatic organisms. In Europe, the regulations on agricultural pesticide usage are currently focusing on “classical” pesticide transport pathways, such as surface runoff, spray drift into surface waters, or tile drainage flow. Recent studies have shown that in certain cases also so-called <em>hydraulic shortcuts</em> (e.g. road storm drains, or manholes of the tile drainage systems) can be of major importance for pesticide transport into surface waters. However, until now research has widely neglected this transport pathway.</p><p>In this study, we investigated the relevance of hydraulic shortcuts for the pesticide transport from arable land to surface waters in Switzerland. We selected twenty small catchments throughout the Swiss midlands as study areas by performing a weighted random selection on a nation-wide hydrological catchment stratification dataset. On average, they have an area of 3.5 km<sup>2</sup> with a fraction of 44 % of arable land. In the agricultural areas of these catchments, we mapped hydraulic shortcuts using different data sources: Field surveys, high-resolution aerial images captured by a fixed-wing drone as well as plans of the road storm drains and the tile drainage systems. Subsequently, we modelled the hydrological connectivity of arable areas to surface waters using a digital elevation model and a D-infinity flow direction algorithm. Within this model, we distinguished between areas with a direct and indirect (i.e. via shortcuts) surface water connectivity.</p><p>Our model results show that major fractions of the arable areas with surface water connectivity are not connected directly, but via hydraulic shortcuts: The fraction of indirectly connected areas ranges between 18 % and 90 %, with a median of 52 % for the 20 catchments. In order to check the model robustness we performed sensitivity analyses for different model parameters, such as sink filling depth, maximal flow length, or parameters addressing the influence of roads, forests, and hedges. In certain cases, changes of those model parameters have a strong influence on the absolute extent of directly and indirectly connected areas. However, their fractions compared to the total connected area were insensitive to changes in the model parameters.</p><p>In addition, we will present the results of a model predicting the fraction of arable land connected to shortcuts within a catchment, depending on auxiliary quantities (e.g. length of roads of a certain type, land use, slope). Using this model, we can estimate the arable land fraction per catchment on a national scale.</p>

Surface water connectivity of seasonal isolated lakes in a dynamic lake-floodplain system

Surface water connectivity dynamics of a large scale extreme flood

Developing a conceptual model of groundwater – Surface water interactions in a drought sensitive lowland catchment using multi-proxy data

The long-term record of glacial/interglacial cycles indicates three major paleoceanographic regimes in the Norwegian Sea. The period since the first major glaciation over Scandinavia at 2.56 Ma is characterized by high-frequency, low-amplitude oscillations of ice-rafted debris inputs, a lowered salinity, and decreased carbonate shell production in surface waters as well as overall strong carbonate dissolution at the sea floor. These conditions indicate a more zonal circulation pattern in the Northern Hemisphere and a relative isolation of surface and bottom waters in the Norwegian Sea. The generally temperate glacial climate was only interrupted by episodic weak intrusions of warm Atlantic waters. These intrusions have been detected in considerable magnitude only at Site 644, and thus are restricted to areas much closer to the Norwegian shelf than during earlier periods. The interval from 1.2 to 0.6 Ma is characterized by an increase in carbonate shell production and a better preservation, as well as a change in frequency patterns of ice-rafted debris inputs. This pattern reflects increasing meridionality in circulation-strengthening contrasts in the Norwegian Sea between strong glaciations and warm interglacials. The past 0.6 Ma reveal high-amplitude oscillations in carbonate records that are dominated by the 100-k.y. frequency pattern. Glacial/interglacial sedimentary cycles in the ODP Leg 104 drill sites reveal a variety of specific dark lithofacies. These dark diamictons reflect intense iceberg rafting in surface waters fed by surges along the front of marine-based parts of the continental ice sheets in the southeastern sector of the Norwegian Sea and are associated with resuspension of reworked fossil organic carbon and strong dissolution at the sea floor. Piling up of huge iceberg barriers along the Iceland-Faeroe-Scotland Ridge might have partially blocked off surface water connections with the North Atlantic during these periods.

Surface water connectivity controls fish food web structure and complexity across local- and meta-food webs in Arctic Coastal Plain lakes

Ecosystem function in rivers, lakes and coastal waters depends on the functioning of upstream aquatic ecosystems, necessitating an improved understanding of watershed-scale interactions including variable surface-water flows between wetlands and streams. As surface water in the Prairie Pothole Region expands in wet years, surface-water connections occur between many depressional wetlands and streams. Minimal research has explored the spatial patterns and drivers for the abundance of these connections, despite their potential to inform resource management and regulatory programs including the U.S. Clean Water Act. In this study, wetlands were identified that did not intersect the stream network, but were shown with Landsat images (1990–2011) to become merged with the stream network as surface water expanded. Wetlands were found to spill into or consolidate with other wetlands within both small (2–10 wetlands) and large (>100 wetlands) wetland clusters, eventually intersecting a stream channel, most often via a riparian wetland. These surface-water connections occurred over a wide range of wetland distances from streams (averaging 90–1400 m in different ecoregions). Differences in the spatial abundance of wetlands that show a variable surface-water connection to a stream were best explained by smaller wetland-to-wetland distances, greater wetland abundance, and maximum surface-water extent. This analysis demonstrated that wetland arrangement and surface water expansion are important mechanisms for depressional wetlands to connect to streams and provides a first step to understanding the frequency and abundance of these surface-water connections across the Prairie Pothole Region.

Surface water and groundwater are often treated as separate entities. However, almost all surface water is in continuous interaction with groundwater. In a few isolated cases there is virtually no interaction between the two, but in the majority of cases there is substantial interaction, albeit highly variable, temporally and spatially. Often surface water streams gain water from groundwater systems, and as a result extractions from groundwater will reduce streamflows. Sometimes the reverse is true, and groundwater is replenished by leakage from the streamflow channels (and/or from inundated floodplains); in these cases it is the withdrawal of water from streams reduces the recharge to groundwater. The interaction between surface water and groundwater is hidden from view, and historically we have tended to manage the two resources separately. As a result we have often double-accounted and even double-allocated the same resource – once as surface water and a second time as groundwater – even though physically we are dealing with the same parcel of water. We have often not recognised this interaction because groundwater moves very slowly beneath the surface. The time taken for groundwater extractions to influence streamflows may range from days to many decades. Thus, the interaction we become aware of today might be the legacy of actions taken many years earlier.

Wetlands are dynamic ecosystems vital for sustaining ecological health and development at regional and global scales. Geospatial tools have emerged as essential for managing wetland ecosystems. This study assessed the spatiotemporal dynamics of water spread in the Point Calimere Wetland, a coastal Ramsar site located along the Bay of Bengal, India, from 1984 to 2023. The analysis based on Global Surface Water Explorer (GSWE) and Normalized Difference Water Index (NDWI) derived from Landsat 5, 7, and 8 data revealed that 21% of the total wetland area showed an increasing trend. In comparison, 5.7% of the area showed a decreasing trend of surface water coverage, largely driven by erosion and climatic variability. The mean water spread increased from 119.47 km2 (2000-2003) to 160.88 km2 (2020-2023), with notable seasonal fluctuations. Among all seasons, the monsoon with the highest surge (41.1%) in water dynamics reported the largest water spread in 2020-2023 (221.87 km2). A moderate positive and negative relationship was noted between rainfall and water spread (r = 0.35) and temperature and water spread (r = - 0.43). A marked increase in habitat patches and edge density between 2000-2003 and 2020-2023 indicates the wetland's vulnerability to changing climatic conditions and the critical role of seawater intrusion, shoreline changes, and tidal forces in shaping its hydrological dynamics. The data presented on the historical water dynamics in this study is invaluable for the conservation planning and management of wetlands to support the associated coastal biodiversity and livelihood of the dependent communities.

Recharge areas of the Guarani Aquifer System (GAS) are particularly sensitive and vulnerable to climate variability; therefore, the understanding of infiltration mechanisms for aquifer recharge and surface run‐off generation represent a relevant issue for water resources management in the southeastern portion of the Brazilian territory, particularly in the Jacaré‐Pepira River watershed. The main purpose of this study is to understand the interactions between precipitation, surface water, and groundwater using stable isotopes during the strong 2014–2016 El Niño Southern Oscillation event. The large variation in the isotopic composition of precipitation (from −9.26‰ to +0.02‰ for δ18O and from −63.3‰ to +17.6‰ for δ2H), mainly associated with regional climatic features, was not reflected in the isotopic composition of surface water (from −7.84‰ to −5.83‰ for δ18O and from −49.7‰ to +33.6‰ for δ2H), mainly due to the monthly sampling frequency, and groundwater (from −7.04‰ to −7.76‰ for δ18O and from −49.5‰ to −44.7‰ for δ2H), which exhibited less variation throughout the year. However, variations in deuterium excess (d‐excess) in groundwater and surface water suggest the occurrence of strong secondary evaporation during the infiltration process, corresponding with groundwater level recovery. Similar isotopic composition in groundwater and surface water, as well as the same temporal variations in d‐excess and line‐conditioned excess denote the strong connectivity between these two reservoirs during baseflow recession periods. Isotopic mass balance modelling and hydrograph separation estimate that the groundwater contribution varied between 70% and 80%, however, during peak flows, the isotopic mass balance tends to overestimate the groundwater contribution when compared with the other hydrograph separation methods. Our findings indicate that the application of isotopic mass balance methods for ungauged rivers draining large groundwater reservoirs, such as the GAS outcrop, could provide a powerful tool for hydrological studies in the future, helping in the identification of flow contributions to river discharge draining these areas.

Intermittent surface connectivity can influence aquatic systems, since chemical and biotic movements are often associated with water flow. Although often referred to as fill and spill, wetlands also fill and merge. We examined the effects of these connection types on water levels, ion concentrations, and biotic communities of eight prairie pothole wetlands between 1979 and 2015. Fill and spill caused pulsed surface water connections that were limited to periods following spring snow melt. In contrast, two wetlands connected through fill and merge experienced a nearly continuous, 20-year surface water connection and had completely coincident water levels. Fill and spill led to minimal convergence in dissolved ions and macroinvertebrate composition, while these constituents converged under fill and merge. The primary factor determining differences in response was duration of the surface water connection between wetland pairs. Our findings suggest that investigations into the effects of intermittent surface water connections should not consider these connections generically, but need to address the specific types of connections. In particular, fill and spill promotes external water exports while fill and merge favors internal storage. The behaviors of such intermittent connections will likely be accentuated under a future with more frequent and severe climate extremes.

Conceptual framework for the main biogeochemical dynamics in the floodplain. Spatio-temporal averaged parameter values are shown inside circles (mg/L for chemical parameters; µS/cm for EC; ‰ for ẟ 2 H). “+” and “-” are the trends of values compared with prior period (i.e., Winter inundation is compared with late Autumn and early winter; Summer drying is compared with winter inundation) • Floodplain hydro-biogeochemical processes were quantified with multi-proxy methods. • High spatio-temporal dynamics in isotopes and biogeochemistry were observed. • The Oder River is main water source for its floodplain, with rainfall as secondary. • Biogeochemical processes control summer solute levels as wetlands are more anoxic. • Groundwater-surface water interactions appear to be of secondary importance. Rivers and their floodplains experience complex, dynamic hydrological regimes resulting in closely-coupled interactions. Like other large floodplains, the Lower Oder Valley National Park, Germany, provides important wetland habitats for fauna and flora but are vulnerable to hydrological disconnection and pollution events, such as the recent water quality disaster in August 2022, where high inputs of mine water caused lethal toxicity levels for fish. This study investigated the role of hydrological connectivity dynamics on biogeochemistry in the Oder river-floodplain system through a multi-proxy approach to quantify water sources, ages and evaporation losses (via water stable isotopes and tritium), water quality (by chemical analysis), as well as surface water (remote sensing) and sub-surface connectivity (geophysical surveys). During elevated levels of the Oder River in winter, open floodgates allow inundation of the floodplain polders delivering a variety of solutes into its associated wetlands. This high connectivity is reflected in low spatial variation in isotopes and hydrochemistry. Solutes are delivered from the Oder River to the floodplain, and water is well-oxygenated (with dissolved O 2 concentrations ∼ 15 mg/L). After flooding recedes, enhanced respiration and photosynthesis in the floodplain intensifies local biogeochemical gradients. Nitrogen is consumed (NO 3 falling from ∼ 4 to ∼ 0.1 mg/L), sulfate (SO 4 2- from ∼ 90 to ∼ 50 mg/L) is reduced, and carbon (DIC increased from ∼ 30 to ∼ 50 mg/L) and phosphorus (SRP increasing from ∼ 1 to ∼ 300 mg/L) are released through the decomposition of organic matter. During this non-inundation period, groundwater discharge to the floodplain’s water bodies is limited and concentrations of chloride and base cations increase in summer due to high evaporation. Low precipitation, dis-connectivity among water ponds in the polders and low groundwater recharge result in high but spatially variable evaporation fractions as reflected by stable water isotopes. We developed a conceptual model of these dynamics of hydrological connectivity and solute transport between the Oder river-floodplain system, and the summer evolution of dominant biogeochemical processes. Understanding these patterns, connections and processes is a prerequisite to sustaining vulnerable wetland habitats under changing climatic, hydrological and water quality conditions.

Surface hydrology of low-relief landscapes: Assessing surface water flow impedance using LIDAR-derived digital elevation models