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.
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.
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.
As regional heterogeneity on the Qinghai Tibetan Plateau (QTP), the “greening rate” between alpine steppe in the west and alpine meadow ecosystems in the east is difference during the past several decades. To investigate the difference, the net photosynthetic rate (An) and the supply (mesophyll conductance ( g m), stomatal conductance ( g s)) and demand (the maximum rates of Rubisco carboxylase activity ( V cmax) and photosynthetic electron transport ( J max)) for CO 2 of three plants functional types (PFTs) were measured. Other functional traits and influencing factors were compared among ecosystems along the altitudinal gradients of QTP. The An of the PFTs was simulated under potential future conditions. At high altitudes, grass was found to maintain a relatively stable An by decreasing V cmax, J max, and g s, while slightly increasing g m, compared with that at a low altitude. The An of sedge and shrubs increased with rising V cmax, J max and g s and g m values, resulting in a large increment in the An at low altitudes. Grass seemed to be less sensitive to the environment by reducing the supply of and holding onto CO 2, while sedge and shrub increased both. Grass and sedge should be divided into two PFTs rather than remaining as one based on their opposite physiological and morphological functions in response to climate change. The ecosystem at 3600 m was transitional. C a was likely to be a more dominant factor than T a in affecting the An of grass. The order of rising An in PFTs was shrub > sedge > grass and the An of alpine meadow was found to increase more under the two future climate scenarios.
Human activities affect the structure, dynamics, and energy flow of aquatic ecosystems. River damming, a common anthropic impact in Brazil, changes solar incidence, water flow, and temperature of waterbodies, thereby affecting their fauna. Due to their high sensitivity to environmental changes, the Odonata may be indicators of these impacts. We sampled two ecologically distinct sites, (1) a quasi-pristine forested area; and (2) a nearby human-impacted reservoir landscape, to evaluate the effects of damming on odonate community structure. The species composition of quasi-pristine communities was more heterogeneous and differed almost completely (indicating high turnover) from that of the reservoir-area communities. The capacity of the reservoir to maintain local fauna was almost nil. The communities in the changed landscape had the highest local diversity, which is related to the high occurrence of widespread generalist South American species. We also tested two recently proposed bioindication ratio tools based on the abundance of high-level taxonomic categories; both effectively demonstrated the extent of the impacts of damming. The best performing ratios were Coenagrionidae/other Zygoptera richness ratio, Zygoptera/Anisoptera abundance ratio, and Libellulidae/other Anisoptera richness ratio. The reservoir landscape promotes biotic homogenization. However, the water supply system entails the preservation of part of the native habitat in its surrounding areas, consequently maintaining local biodiversity in quasi-pristine environments.
As the impacts of the anthropocene intensifies in rivers, there is an increasing need to understand how these changes affect both daily and sub-daily stream flow variability, timing and flow quantities, as these are some of the most influential drivers of spatial and temporal dynamics of stream biota. In this paper, long-term changes in flow patterns of a strategic water source area in an arid region of southern Africa were quantified, focusing on the relation between daily and sub-daily and its potential impact on fish biota of the catchment. Long-term temporal trends in stream flow were modelled using Generalized Least Squares (GLS), while sub-daily and daily mean flow of the same stations were compared using a suite of metrics. Periods of similar stream flow patterns were identified using K-means cluster analysis. A spreadsheet rule-based model was developed linking fish communities to streamflow patterns providing a predictive framework for fish assemblage responses to stream flow classes. Long term reduction in flow has a strong seasonal component, with significant decreases during the wet season, not linked to long-term rainfall patterns. Flow variability has increased over time, while 78% of sub-daily flow metrics were related to daily flow metrics. Oscillating flow conditions and the loss of intermediate flow states may permanently exclude certain fish flow guilds. However, temporal partitioning is only evident when sub-daily metrics are considered, highlighting their importance for assessing ecological resilience.
The study was conducted in Lake Baringo and determined quantitative relationships between water level changes, water quality, and fishery production for informed lake basin management. Long-term (2008 to 2020) data on water level, water quality, and fisheries yields from Lake Baringo were analyzed using a combination of statistical methods. Linear and waveform regression analyses described patterns of lake level fluctuations over time while, Pearson’s correlation determined the concordance of lake level changes with water quality parameters, landings, and condition of fish species. PCA results grouped the study period into different years based on annual water quality variable levels. LOWESS analysis showed the decline of annual lake level amplitude over time with peak values in 1964 (8.6 m) and 2008 (9.4 m). The waveform regression significantly modeled lake level fluctuations as indexed by annual deviations from the long-term average (DLTM) and showed a 20-year oscillation between peak water levels in the lake. There were significant positive correlations of Water Level Fluctuations (WLFs) with water quality variables and water quality index (WQI) in Lake Baringo. Linear regression analyses showed a significant concordance (p < 0.05) between the annual fishery yield and the rising WLFs (r = 0.66). Overall, the results demonstrate that WLFs of Lake Baringo are a driver of fish species biomass and physico-chemical properties of the lake. We recommend the integration of fisheries yields, water quality assessment, and WLFs modeling at different temporal scales in the management of Afrotropical lake ecosystems
Water scarcity in the southeastern United States has increased in recent decades due to population growth, land use intensification, and climate variability. Precipitation is relatively abundant, but declines in streamflow suggest a need to better manage water yield. Restoration of low-density, frequent-fire longleaf pine (Pinus palustris Mill.) woodlands, which once dominated the southeastern Coastal Plain, represents a possible strategy to increase water yield and mitigate water scarcity. The Flint River Basin has seen recent conflicts over water appropriations and lies within the historic range of longleaf pine. We used the Soil and Water Assessment Tool (SWAT) to evaluate the potential effect of longleaf pine restoration on streamflow in the Ichawaynochaway Creek, a major tributary of the Flint River. Parameters governing plant water use, e.g. leaf area and leaf physiology, were adjusted to create a longleaf pine land cover. We simulated the conversion of ~95,000 ha of existing forest to longleaf pine, an increase from 3% to 35% of landcover in the basin. Modeled evapotranspiration was lower for longleaf pine compared to other forest types in the region, and conversion to longleaf pine increased annual water yield by 17.9 ± 1.6 mm, or 5.2%. Proportional changes in monthly streamflow were up to 74% higher during low flow periods, when in-stream habitat is most vulnerable. Restoration of longleaf pine could be a promising way to mitigate water scarcity in the southeastern U.S., and adding flow during extreme droughts may prove vitally important for conserving imperiled aquatic organisms.