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.

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

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.

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 Marius G. Floriancic. Click on the document to view its contents.

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.

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.

Analytical tools are needed to identify and quantify artificial short- and long-term discharge fluctuations, which can disrupt the natural processes of a river. To measure the properties of discharge magnitude, frequency, duration, timing and flow change, such tools typically use a subset of metrics selected from over 170 descriptive statistical indices. Many metrics are based on multi-day mean or median discharges with associated variance or use a single value to describe the entire dataset. However, these source indices do not quantify the temporal configuration of streamflow, an additional hydrologic property that is often overlooked. To address this situation, a non-index approach to quantify all streamflow properties has now been developed using analysis methods based on the lag (1) temporal autocorrelation signature of the streamflow. The discharge (Q), discharge change (dQ/dt), and rate of discharge change (d 2Q/dt 2), along with sequential summations, are presented in novel infographics. A dam release river impact case study for the Colorado River at Lees Ferry, Arizona, is included to demonstrate this innovative way of analyzing streamflow datasets. The result is a set of new tools which yield detailed information about the hydrologic regime, are highly customizable, and can either be used as a stand-alone analysis or be integrated into other existing data analysis techniques. The end result is a better understanding of the hydrologic regime, more focused research, and more effective management planning.

Groundwater is an important global resource, providing water for irrigation, industry, geothermal uses, and potable water all over the world. Moreover, groundwater contains the world’s largest terrestrial freshwater biome. Groundwater faunal communities undertake important ecosystem services including the provision of clean water. Despite this, investigations on the spatial and temporal variations and the influence of environmental parameters on these organisms, are still rare. The aim of this study is to provide a global overview on groundwater fauna (stygofauna) research, including the historical evolution of research topics and development of sampling methods. To achieve this, an extensive review of accessible groundwater fauna data was conducted. Over time, there has been an exponential increase in the number of studies together with changing paradigms in the research focus, particularly as sampling methods have developed and molecular analyses become common. Studies on groundwater fauna are spatially uneven and are dominated by studies in Europe and Australia, with few studies in Africa, Asia and the Americas. This has resulted in a potential geographic and climatically biased global view of stygofauna and groundwater ecology. In the future, a more evenly distributed sampling effort in underrepresented areas is necessary to enable global studies, thus allowing a more comprehensive perspective on stygofauna biodiversity, roles, and functional significances. This is increasingly important with the accumulating knowledge of the sensitivities of these ecosystems to anthropogenic activities, including climate change, and is fundamental to effective management of these ecosystems.

Restoration of natural secondary forests and afforestation of introduced tree species are major effective measures for revegetation. The semi-arid Loess Plateau region, characterized by fragile ecosystems and severe soil erosion, is a key area for ecological restoration and protection in China. To illustrate water use characteristics and adaptation to drought in the main forests in this area, we monitored the xylem sap flow of two typical forest communities, a secondary natural forest dominated by oak ( Quercus liaotungensis) and a pure plantation of black locust ( Robinia pseudoacacia), during 2011‒2019 using Granier-type thermal dissipation probes. Solar radiation, air temperature, relative humidity, precipitation, and soil water content were measured simultaneously. Throughout the whole study period, the mean diameter at breast height and total sapwood area increased by 4.5 cm and 1.10 m 2 ha -1 in the oak forest and by 1.0 cm and 0.22 m 2 ha -1, respectively, in the black locust plantation. The monthly stand transpiration was jointly determined by phenological and meteorological factors. At the annual timescale, transpiration of the oak stand was significantly correlated with potential evapotranspiration and rainfall in the previous year, whereas a significant positive relationship was detected between stand transpiration and soil water content in the black locust stand. The analyses of differences between dry and wet years showed that, the oak forest exhibited significantly different parameters in the regression analysis of stand transpiration to vapor pressure deficit. While only one parameter was clearly distinct in the black locust plantation, suggesting that its transpiration status did not fully recover even in wet years. The management of black locust plantations with weakened growth conditions should be adjusted under prolonged drought conditions. In contrast, oak forest can maintain the water balance and stable growth by efficiently controlling stomatal behavior.

Analyzing the dynamics of landscape connectivity is of great significance for biodiversity conservation, but the description of multiple ecological processes and the depth of coupling requires to be strengthen. Taking the grassland of Poyang Lake as a case, based on the integrated perspective of habitat and biology, comprehensively considering the ecological process of water level change and species diffusion, this study firstly analyzed the changes of landscape connectivity of grassland with different water levels and diffusion distances by using the graph-based connectivity indices. then, landscape pattern indices were applied to analyze the dynamics of landscape pattern of grassland and further study the effects of landscape pattern on connectivity. The results showed as follows: (1) From the perspective of habitat, grassland connectivity showed a sharp decrease with the increase of water level. From the perspective of ecology, the species diffusion distance had an absolutely positive impact on landscape connectivity. With the increase of diffusion distance, grassland connectivity increased significantly. (2) The dynamics of landscape pattern of grassland showed that with the increase of water level, the patch area shrank, the patch shape tended to be simple, the patch density decreased and the patch fragmentation aggravated. (3) The correlation results between landscape pattern and connectivity indicated that F had a significant positive relationship with PD, ED, PC had a strong significant positive relationship with LPI, COHESION, and NC had a negative relationship with LPI, ED, COHESION. This study provides theoretical guidance for the conservation and management of grassland in Poyang Lake.

The forest-floor litter layer can retain substantial volumes of water, thus affecting evaporation and soil-moisture dynamics. However, litter layer wetting/drying dynamics are often overlooked when estimating forest water budgets. Here we present field and laboratory experiments characterizing water cycling in the forest-floor litter layer, and outline its implications for subcanopy microclimatic conditions and for estimates of transpiration and recharge. Storage capacities of spruce needle litter and beech broadleaf litter averaged 3.1 mm and 1.9 mm respectively, with drainage/evaporation timescales exceeding 2 days. Litter-removal experiments showed that litter reduced soil water recharge, reduced soil evaporation rates, and insulated against ground heat fluxes that impacted snowmelt. Deadwood stored ~0.7 mm of water, increasing with more advanced states of decomposition, and retained water for >7 days. Observed daily cycles in deadwood weight revealed decreasing water storage during daytime as evaporation progressed and increasing storage at night from condensation or absorption. Water evaporating from the forest-floor litter layer modulates the subcanopy microclimate by increasing humidity, decreasing temperature and reducing VPD. Despite the relatively small litter storage capacity (<3.1 mm in comparison to ~10 2 mm for typical forest soil rooting zones) the litter layer alone retained and cycled 18% of annual precipitation, or 1/3 of annual evapotranspiration. These results suggest that overlooking litter interception may lead to substantial overestimates of recharge and transpiration in many forest ecosystems.

Blue-green spaces composed of water and green spaces have certain ecological, economic, and social benefits for urban development. Many evaluation index systems have been developed to evaluate the health status of urban ecosystems. However, in these evaluation index systems, blue and green spaces are separately evaluated without considering the synergistic effect between water and green spaces in the ecosystem, thus affecting the unified planning and construction of cities. Therefore, based on existing studies, the development process of the blue-green space evaluation index system is divided into three stages: supply service evaluation stage, adjustment service evaluation stage, and cultural service evaluation stage in order to deeply discuss the development path of the blue-green space evaluation index system. The single blue and green evaluation index systems are compared from the perspectives of index selection and evaluation content. Moreover, the characteristics of conventional evaluation methods are discussed in order to propose an applicable evaluation index system and evaluation method of blue-green spaces for evaluating the degree of blue-green integration of cities. The review provides the basis for urban planning and ecological restoration.

Our understanding of the hydrological processes in cocoa agroforests is extremely limited. Most work has focused on characterising throughfall and transpiration processes under various management approaches and climate change scenarios. However, little is currently understood about the soil hydrological processes which serve as a link to throughfall and transpiration. We monitored the soil properties, soil water repellency and hydraulic conductivity in a 5, 12 and >30 year old cocoa plantation in the wet and dry seasons. During the wet season repellent conditions were absent in all stands while the hydraulic conductivity showed no significant differences among them. This suggests that stand age has little effect on water movement during the wet period. During the dry season, the soil at the 5 and 12 year old stands became extremely repellent and was twice as severe as that of the >30 year old plantation. It was expected that the extreme repellency in the younger stands would reduce infiltration rates; however, higher rates were recorded in the 5 and 12 year old stands. This was likely due to the combination of a repellent soil matrix and the presence of large, deep soil cracks which enhanced preferential flow. As the repellency was not significantly correlated with soil properties, we hypothesised that the high grass/sedge cover and temperatures in the 5 and 12 year old stands enhanced it. While further research is needed to investigate the role that grass and sedges play in developing repellent conditions, managing their cover may prove beneficial for the growth and survival of young cocoa trees.

Tracer-aided studies to understand source water partitioning in tropical ecosystems are limited. Here we report dry season source water partitioning in five unique ecosystems distributed across Costa Rica in altitudinal (<150-3,400 m asl) and latitudinal (Caribbean and Pacific slopes) gradients: evergreen and seasonal rainforests, cloud forest, Páramo, and dry forest. Soil and plant samples were collected during the dry season (2021). Plant and soil water extractions (triplicates) were conducted using controlled centrifugation. Stem water extraction efficiency and stem water content were calculated via gravimetric measurements. Water source contributions were estimated using a Bayesian mixing model. Isotope ratios in soil and stems exhibited a strong meteoric origin. Enrichment trends were detected mainly in stems and cactus samples within the dry forest ecosystem. Soil profiles revealed nearly uniform isotopic profiles; however, a depletion trend was observed in the Páramo ecosystem below 25 cm depth. More enriched compositions were reported in cactus samples for extracted water volumes above ~20% ( Adj. r2=0.34, p<0.01). The most prominent dry season water source in the evergreen rainforest (74.0%), seasonal rainforest (86.4%), and cloud forest (66.0%) corresponded with soil water. In the Páramo ecosystem, recent rainfall produced by trade wind incursions resulted in the most significant water source (61.9%), whereas in the dry forest, mean annual precipitation (38.6%) and baseflow (33.1%) were the dominant sources. The latter highlights the prevalence of distinct water uptake sources between recent cold front’s rainfall to more well-mixed soil moisture during the dry season.

Peatland microtopography contains hummocks (local high points) and hollows (local low points). Little is known about how the evapotranspiration (ET) of peat (P), peat-bryophyte (BP), peat-litter (LP) and peat-bryophyte-litter (LBP) columns varies with peatland microforms. That is, whether there are fine-scale variations in peatland evaporation, and if they are critical when being upscaled to the entire peatland ecosystem is yet to be answered. This study found that ET was significantly affected by cover type (P, BP, LP or LBP) and the interaction effect of the cover type and microform, based on the field evaporation experiments in a montane peatland in the Canadian Rocky Mountains, during the growing season of 2021. Mean daily ET of P-Hummock and P-Hollow is 14.16 and 11.76 g d -1, respectively; BP-Hommock and BP-Hollow is 9.57 and 14.38 g d -1, respectively; LBP-Hummock and LBP-Hollow is 9.44 and 9.91 g d -1, respectively; and evaporation of LP-Hummock and LP-Hollow is 5.68 and 7.64 g d -1, respectively. Peatland microform indirectly affected ET through interactions with cover type, modifying the vertical profile of soil temperature, and changing key environmental drivers of evaporation. Moreover, the ability of two widely used models in modelling the spatial variation of peatland evaporation were also tested. It was found that Penman-Monteith (P-M) model and the bryophyte layer model in the Atmosphere-Plant Exchange Simulator (APES) were able to yield satisfactory results based on field measurements of soil temperature and soil moisture. This study supports developing more practical evaluation tools on the hydrological state of peatland ecosystems.

Hydropeaking (the release of water pulses at hydropower plants) results in temporary reductions in river channel water-covered area downstream, which may cause fish mortality through stranding. We used a mechanistic modelling approach to examine how, both, the form of the hydropeaking cycle, and the characteristics of the affected fish, control how hydropeaking may cause stranding mortality of fish. We modelled the response of Atlantic parr to hydropeaking in a regulated watercourse in central Norway (the River Nidelva) using an individual-based population model designed explicitly to examine fish behavior and stranding mortality during hydropeaking. A response to hydropeaking, involving migration from the river banks toward the mid-channel on down-ramping, and a return to the river banks on up-ramping, was based on individuals being parameterized to migrate to habitat properties that spatially changed throughout the hydropeaking cycle. We found that stranding mortality was strongly dependent on both the form of the hydropeaking cycle and on the fish response. Total stranding mortality was more dependent on the down-ramping speed than the duration of the minimum flow period. Total stranding mortality was greatest when there was a low movement speed, leading to individuals being stranded, combined with a high probability of dying per unit of time when stranded. Given the sensitivity of mortality to the fish response, and the lack of detailed field studies quantifying this, we conclude that this area requires further controlled studies for parameterizing models used to predict effects of hydropeaking on fish.

Evapotranspiration (ET) constitutes the largest loss of water from subtropical grassland and wetland ecosystems, yet data in much of the world have high uncertainty at the landscape scale as there is little information on plant water use. Additionally, anthropogenic alterations to grasslands are a major threat globally and alter ecosystem water use, but the impact of these changes is often unquantified. A major reason for this is the complexity and expense of field-based ET quantification methods such as agricultural lysimeters and eddy covariance systems. Accurate measurements of ET are critical for sustainable water management. This study developed two different low-cost lysimeters – weighing-type and water level based, to measure ET under controlled conditions for single species as well as mixed grassland and wetland communities. Lysimeters were placed in an open sided shadehouse with a transparent roof to exclude rainfall. ET values were then compared with (i) Actual ET measurements from an eddy covariance tower onsite, (ii) vapor transport-based ET models – FAO Penman-, Modified Turc and Abtew Simple Radiation models, and (iii) ET data from the Florida Automated Weather Network. Both weighing-type and water level lysimeters showed seasonal patterns and annual magnitudes similar to the other ET methods. Annual ET measurements from weighing-type lysimeters (881-1278 mm for four plant species, n=5 per species, 20 in total) and water level lysimeters (1085 mm, plant community average, n = 31) were similar to model estimates (1000-1200mm). Actual ET from eddy covariance was 722 mm for ten months (missing data for February and March), while lysimeter measurements for the dominant grass Paspalum notatum was 885mm for the same 10 months. Low-cost lysimeters can inform regional ET models/remote sensing data lacking field validation and thus are potentially useful for water resources and ecosystem management in data-poor regions of the world.