Hypoxic zones and associated nitrate pollution from farms, cities, and industrial facilities is driving declines in water quality that affect ecosystems, economies and human health in major rivers and coastal areas worldwide. In the Mississippi River, the United States Environmental Protection Agency set a goal of reducing nitrogen loading 20% by 2025 but estimating progress toward this goal is difficult because data from in-stream gauges and laboratory samples are too sparse. Satellites have the potential to provide sufficient data across the Mississippi River, if a key methodological challenge can be overcome. Satellites provide data from visible light, but nitrates are only observable with ultraviolet light. We address this methodological challenge by using a two-step surrogate modeling procedure to link optical data and nitrates in the Lower Mississippi River. First, we correlate in-situ nitrate measurements to common water quality parameters, particularly turbidity and chlorophyll, using data from water sensors installed at Baton Rouge, Louisiana, USA, and a long-term data set from Louisiana State University. Second, we correlate these water quality data to satellite estimates of water quality parameters. We found a correlation between these water quality parameters and nitrate concentrations, as indicated by a coefficient of determination, when the relationship was viewed in non-linear parameter space. The spatial extent of the correlation was tested with an upstream nitrate sensor 140 km north of the estimation location. These results provide proof-of-concept that we can develop models that use satellite data to provide large scale monitoring of nitrates across the Mississippi River Basin and other impaired rivers, globally.

Changes in water and nitrogen availability can affect the structure and function of arid ecosystems. How these resources affect aboveground primary productivity (ANPP) remains far from clear. We examined the N and water limitation of ANPP from the species to the community level and the response of ANPP to annual precipitation in a Patagonian steppe. We conducted a 7-year field experiment with water addition (+W), nitrogen addition (+N), and +NW. Destructive methods for grasses and allometric relationships for shrubs were used to assess ANPP and vegetation indices (NDVI and MSAVI2) to estimate community ANPP. An increase in ANPP of one grass species ( Papposstipa humilis) and a decrease of the grass Poa ligularis under +N were observed. Some shrubs species exhibited mortality under nitrogen addition. Nitrogen exerted a positive effect on grass ANPP and amplified the sensitivity of grass ANPP to annual precipitation. However, +N had not effects on the shrub ANPP and shrub ANPP-precipitation relationship. Water addition by itself had no effect on ANPP for either shrubs or grasses. However, shrubs responded positively to an unusually wet year regardless of treatment and were also more sensitive to changes in annual precipitation than grasses. Total ANPP increased significantly in +N relative to the C and +W, but without changes in the sensitivity to annual precipitation. The results suggest that the responses of grasses and shrubs to water inputs is driven by soil moisture redistribution and rooting depth and that grass and community ANPP is more limited by N than by water.

The ecological restoration projects (ERPs) sig[1](#fn-0002)nificantly affect the water conservation function (WCF) of the Taihang Mountain area. However, a comprehensive understanding of the ecological effects of water conservation (WC) in different ecological engineering (EE) areas still needs to be improved, which limits the optimization and implementation of ERPs in semi-arid climate areas. In this study, we employed the integrated valuation of ecosystem services and trade-offs (InVEST) model to evaluate the differences in WCF among different ERPs in the Taihang Mountain area. Additionally, we used the structural equation model (SEM) to explore the influence of various factors on WCF, including EE factors. The results showed the following: (1) The total amount of WC in the Taihang Mountain area increased yearly from 2000 to 2020, with an 85.25% increase in 21 years. The WCF showed a trend of transferring to a higher level. (2) The forest recovery (FR) project showed the highest average WC, followed by the grassland recovery (GR) project. FR and GR together provided 61.12% of the WC amount in the EE area. The cropland recovery (CR) project increased the WC by 22.85% compared with the non-ecological engineering area. The WC capacity of the 21-year artificial forest could only reach 70.92% of the natural forest. FR was found to be the most potential ecological restoration type, while CR and GR were the most effective. (3) The enhancement of WCP in the study area resulted from multiple factors. The composite variable SEM revealed four main factors affecting WC (R 2 = 0.427), ranked as follows: climate change > site conditions > EE > society-economy (0.390 > 0.247 > 0.177 > 0.043), of which the EE factor accounted for 20.65%. Precipitation and root depth were the most critical factors affecting WCP, according to the random forest model. (4) The impact of EE on WC varied with altitude, and the effect of the hilly zone was 1.5 times that of the sub-alpine zone. Therefore, the WC effect of ERPs is different due to different types and regions. EE measures should be optimized according to the actual situation to cope with the uncertainty of WC caused by probable extreme climate in the future. Overall, our study provides scientific support for evaluating the impact of ERPs on WCF in semi-arid areas of China.

A document by Hannah A. Varani. Click on the document to view its contents.

The spatiotemporal variability of groundwater level (GWL) is an important property of peatland hydrology that directly affects fluctuations of water storage. Nonetheless, current understanding of the variations of GWL in different time scales still remains unclear. In this study, two peatland watersheds (0.151 km 2 for W1 and 0.844 km 2 for W2) in the Zoige Basin in the Source Region of the Yellow River (SRYR) were selected for monitoring the temporal variability of GWL using self-recorded water loggers during 2017-2021. The main results demonstrate that: (1) GWL variations tended to be controlled by gully drainage in sites adjacent to the gully and be more synchronized with rainfall in sites distant from the gully. The GWL near the gully that cuts through the peat layer was lower than that near the gully without cutting through the peat layer, with a maximum difference between the former and the latter of 58.3 cm, indicating the effect of longitudinal attenuation of the GWL in W1. (2) Because rainfall had a lag effect on the GWL, the length of lag gradually decreased with increased rainfall intensity (i.e., the lag time of sites far away from the gully was about 18 min shorter than that of sites close to the gully in W1). (3) The peak values of the GWL occurred simultaneously with the maximum and minimum rainfall in W2, and the peak occurrence time was related to the ratio of precipitation to evaporation. In the downstream sites, GWL fluctuated more intensively than the upstream ones in W2. Moreover, the average GWL of the upstream sites was 14.3 cm higher than that of the middle ones, indicating a decreasing trend of water storage along the gully. (4) The GWL discrepancy between wet and dry seasons was explicit, but the difference was smaller in the upstream sites due to limited gully incision and higher water storage within the peat layer. Additionally, rainy days dominate the GWL change in wet and dry seasons, but the different rainfall intensity resulted in a stable GWL in the dry season and an oscillating GWL in the wet season in W2. This study uncovers the spatio-temporal variation of groundwater level in two peatland watersheds, which is of great significance for understanding runoff variation, ecohydrological processes, and wetland shrinkage in the SRYR.

1. The flow regime of a river is well established as being one of the key drivers of riverine ecosystem type, diversity and condition. This is especially true of seasonal rivers that experience a cease to flow period over the dry months of the year. 2. In order to effectively assess changes to the flow regime, it is required that flow data be quantified into metrics for ease of assessment and to effectively relate changes to environmental outcomes. 3. Previous methods have used large numbers of, often complex, flow metrics to assess the flow regime. These metrics are often highly internally correlated with each other which may pose problems when considering how these metrics are assessed. The metrics are also often complicated which introduces issues for communication of results. We suggest that due to high internal correlation between metrics, significantly fewer metrics are required to describe the flow regime, and owing to the high correlation within same season flow metrics, simple metrics can be selected. 4. We report on a series of six flow metrics that cover the whole of the flow regime, that are reported annually and that are simple to assess and interpret. We then apply those six metrics to establish environmental water requirements for the North Para River in the Barossa Valley of South Australia. 5. Environmental water requirements are defined using upper and lower bounds of a moving average for each metric, rather than a defined threshold. We suggest this better reflects the highly variable nature of seasonal rivers, and the subsequent tolerances of the flora and fauna that inhabit them.

Water transport timescales (WTTs) quantify how long it takes for water to travel through or remain in a system and are often cast as indicators of ecosystem function and health. Such timescales are known to be affected by vegetation in various environments. We quantify the impact of floodplain vegetation on WTTs within the Wax Lake Delta (WLD), a river delta system in Louisiana, USA, using a high-resolution Delft3D Flexible Mesh (DFM) model incorporating vegetation-induced flow resistance. We show that increased vegetation density leads to extended WTTs within vegetated sections of WLD while fostering flow localization and accelerating transport within distributary channels. We find that the presence or absence of floodplain vegetation significantly influences the volumetric flow directed toward the floodplain, with spatial distribution exerting more control than vegetation density. Vegetation density and spatial arrangement have minimal impact on flow directed out of the deltaic floodplain, indicating that vegetation does not constrain flow across the bayward boundary. Floodplain vegetation strongly influences local-scale transport timescales within the deltaic floodplain but minimally affects water age distributions within distributary channels. Furthermore, network-scale water age distribution remains largely unaffected by vegetation density and spatial arrangement, except for slight modifications in the heavy right tail of the distribution. These findings contribute to a better understanding of how vegetation affects deltaic hydrology across scales, highlighting the importance of considering multi-scale vegetation influences for coastal restoration and management strategies.

Terrestrial water energy coupling (WEC), in the form of the non-linear relationship between Soil Moisture (SM) and evaporative fraction (EF, ratio of actual and potential evapotranspiration), controls critical ecohydrological processes. We investigate and parameterize the evolution of global SM–EF coupling from the field to remote-sensing (RS)-footprint. The field-scale EF and SM were obtained from 163 eddy covariance (EC) and SM sensors at various network (Texas Water Observatory and FLUXNET) sites around the globe. Remote-sensing (RS)-scale EF and SM estimates were obtained from Moderate-resolution Imaging Spectroradiometer (MODIS) and Soil Moisture Active Passive (SMAP) sensors, respectively. We estimate the effective thresholds of the WEC regimes from both EC and satellite datasets to highlight the influence of subgrid-scale heterogeneity, scaling, and observational constraints on the evolution of WEC regimes from field to RS-footprint scale. We compare the critical WEC thresholds of the water- and energy-limited regimes with an SM drydown-based approach and highlight the similarities between both methods in partitioning dominant WEC regimes. EF and SM are strongly coupled in dryland arid and semi-arid regions compared to humid climates. WEC regimes and thresholds have strong interseason variability due to dynamic interactions between soil, vegetation, and atmosphere at the RS-footprint scale. In contrast, field-scale SM-EF coupling is influenced predominantly by agricultural /land-use practices and soil conditions. Hence, future development of Earth-System/Land-Surface models must account for the inter-scale differences in the coupling between terrestrial water and energy fluxes representative of the “ effective” processes at large spatial scales.

The dominant plant species in many African wetlands is Cyperus papyrus. Its adaption to saturated and low oxygen conditions and its dense structure and height provide breeding and feeding grounds for unique flora and fauna. As a keystone species adapted to local hydrology, the flow regime of papyrus offers the full range of hydrologic conditions and events essential to ecosystem health. However, no study has attempted to link papyrus wetlands’ flow regimes to their biologically-relevant hydrologic attributes. The Indicators of Hydrologic Alteration (IHA) enable the evaluation of changes to flow regimes by examining hydrologic records and linking them to biologically-relevant hydrologic characteristics through the Environmental Flow Components (EFCs) approach. This study assesses hydrologic alterations of a papyrus wetland’s flow regime due to rice irrigation. We develop a conceptual ecological model linking papyrus to hydrologic attributes to determine the consequences of changed EFCs (extreme low flows, base flow, high flow pulses, and small and large floods) on papyrus as a habitat. We find that agricultural water management considerably alters the magnitude, duration, timing and rate of change of EFCs for the irrigated area to catchment area ratio greater than 1:153, affecting both sexual and asexual reproduction in papyri plants. Overall, a better understanding of the threats of water diversion for agriculture is made by linking papyrus’ flow regimes to biologically-relevant hydrologic attributes. Knowledge of the roles of the various EFCs could provide opportunities for conserving and protecting papyrus wetlands, especially for systems at risk of altered flows.