Seasonal Water Use Patterns Research Articles

Spatial and seasonal patterns of water use in Mediterranean coastal dune vegetation

AimsThis paper examines the water dynamics of a coastal dune plant community, addressing spatial and seasonal variations. We aimed to detect the patterns of water use by plants at the community level according to their distribution across a coastal dune gradient from beach to inland.MethodsFive sites were established: upper beach, embryo-dune, slack, foredune, and inland. Eight perennial species were collected seasonally to analyse the isotopic composition and water potential. Soil water samples at 3 depths, groundwater, and atmosphere, were obtained to determine plant water sources.ResultsThe species from Inland and foredune plant communities, Retama, Juniperus, and Helichrysum, showed the most stable isotopic signal throughout the year. On the contrary, the species most abundant on the upper beach, embryo-dune, and slack (Ammophila, Achillea, and Polygonum) showed the highest variability. Water deficit decreased the dependence on shallow and mid-soil layers along the beach-inland gradient. Beach and embryo-dune sites showed less negative leaf water potential values than the other positions in the dune gradient.ConclusionsThree factors mark the proportion of water sources used for vegetation in coastal vegetation: community composition, distance to the sea, and seasonality. Coastal dune vegetation exhibited a species-specific response in water uptake that was modified by its location on the gradient. From upper beach to inland, the plant communities showed a slight progressive increase in the use of water from deeper layers. This pattern was similar and overlapped with the wet to dry seasonal pattern.

Blue and Grey Water Footprints of Dairy Farms in Kuwait

In Kuwait, dairy farming faces challenges due to its significant water demands. The current study assessed seasonal patterns of water use to estimate the blue water footprint (WF) and grey WF per kg of fat protein corrected milk (FPCM) for confined dairy farming systems in Kuwait. Blue and grey WFs were evaluated using data from three operational farms. The average blue WF (L·kg-1 FPCM) was estimated to be 54.5 ± 4.0 L·kg-1 in summer and 19.2 ± 0.8 L·kg-1 in winter. The average grey WF (generated from milk house wastewater) was assessed on bimonthly basis and determined based on its phosphate (PO4) concentration (82.2 ± 14.3 mg·L-1) which is the most limiting factor to be 23.0 ± 9.0 L·kg-1 FPCM d-1. The outcomes indicate that enhancing the performance of dairy cows and adopting alternative water management strategies can play a role in minimizing the impacts of confined dairy farming systems in Kuwait on water quality and quantity.

How energy and water availability constrain vegetation water-use along the North Australian Tropical Transect

Energy and water availability were identified as the first order controls of evapotranspiration(ET) in ecohyrodrology. With a ~1,000 km precipitation gradient and distinct wet-dry climate,the North Australian Tropical Transect (NATT) was well suited for evaluating how energy andwater availabilities constrain water use by vegetation, but has not been done yet. In this study,we addressed this question using Budyko framework that quantifies the evapotranspiration as afunction of energy-limited rate and precipitation. Path analysis was adopted to evaluate thedependencies of water and carbon fluxes on ecohydrological variables. Results showed that themajor drivers of water and carbon fluxes varied between wet and dry savannas: down-wellingsolar radiation was the primary driver of the wet season ET in mesic savanna ecosystems, whilesoil water availability was the primary driver in inland dryland ecosystems. Vegetation cansignificantly regulate water and carbon fluxes of savanna ecosystems, as supported by thestrong link of LAI with ET and GPP from path analysis. Vegetation structure (i.e. the tree:grassratio) at each site can regulate the impact of climatic constraint on ET and GPP. Sites with a lowtree:grass ratio had ET and GPP that exceeded sites with high a tree:grass ratio when the grassyunderstory was active. Identifying the relative importance of these climate drivers andvegetation structure on seasonal patterns of water use by these ecosystems will help us decideour priorities when improving the estimates of ET and GPP.

Nitrate-nitrogen patterns in the Raccoon River Basin related to agricultural practices

Nitrate-N concentrations in the Raccoon River have increased beginning in the early 1970s. Since this river is the predominant water supply for the City of Des Moines in Iowa, there is concern about the potential long-term impacts of these trends. Improvements in water quality from agricultural watersheds are critical to protect the water supply, and understanding the factors affecting water quality will lead to potential changes in agricul- tural management to improve water quality. The historical database of nitrate-nitrogen (NO 3 - N) concentrations sampled at the Des Moines Water Works were combined with observa- tions on N fertilizer use, animal production, crop yields, land-use changes, and precipita- tion patterns to evaluate these interrelationships. Mean annual NO 3 -N concentrations in the Raccoon River watershed have been increasing since 1970 in spite of no significant change in N fertilizer use for the past 15 years. There have been three years with maximum NO 3 - N concentrations above 18 mg L -1 . However, these spikes occurred throughout the past 30 years and are not isolated to the last 10 years of record. Nitrate-N loads from the Raccoon River watershed have shown a slight decrease in the past ten years because of the increased crop yields and increased removal of N in the corn (Zea mays L.) and soybean (Gylcine max (L.) Merr.) grains. Production numbers for cattle have decreased by 63% since the early 1980s, while hogs have shown a 20% decrease over the same time period. Therefore, N available for application into the basin has decreased by 25%. Annual variations in NO 3 -N loads are sig- nificantly related to precipitation in the first five months of the year. A significant correlation was found between the land area within the watershed cropped to small grains and hay crops and the increase of NO 3 -N since 1970 (r = -0.76). This relationship was caused by alteration in the seasonal water-use patterns and loss of N during the fall or early spring in the water movement in contrast to corn or soybean, which have a limited N uptake pattern concen- trated between June and early September. Changes in the water-use patterns caused by shifts in cropping patterns provide an explanation for the positive correlation between precipitation and flow during the early part of the year. Development of agricultural management practices that can potentially affect water quality will have to be more inclusive of all components in agricultural systems, rather than only changing fertilizer rate or timing.

A comparison of tree water use in two contiguous vegetation communities of the seasonally dry tropics of northern Australia: the importance of site water budget to tree hydraulics

Tree water use in two contiguous communities (eucalypt open-forest and Melaleuca paperbark forest) was measured in tropical Australia, over a 2-year period. The aims of the study were to (1) quantify daily and seasonal patterns of water use in each community, (2) compare patterns of water use among the communities and (3) compare relationships among tree size, sapwood area and water use within the two contrasting vegetation communities. Access to deep soil water stores and the effect of run-on from the eucalypt forest resulted in a relatively high pre-dawn water potential throughout the year, particularly for Melaleuca forest. There were no differences in daily rates of water use, expressed on a sapwood area (Q s) basis, between the two eucalypt species examined (Eucalyptus miniata Cunn. Ex Schauer and E. tetrodonta F.Muell) at any time in the eucalypt forest. For both the eucalypt and Melaleuca forests, there was less seasonal variation in water use expressed on a leaf area (Q l) basis than on a Q s basis, and neither year nor season were significant factors in Q l. In the mono-specific Melaleuca forest, Q s was not significantly different between years or seasons. Water use on a Q l basis was similarly not significantly different between years or seasons in the Melaleuca forest. Leaf area index (LAI) of the eucalypt forest was about half of that of the Melaleuca forest throughout the year but sapwood area per hectare was 33% larger in the eucalypt than the Melaleuca forest, despite the basal area of the Melaeuca forest being almost double that of the eucalypt forest. There was no significant difference in stand water use (mm day–1) between eucalypt and Melaleuca forests during 1998; however, in 1999 Melaleuca stand water use was larger than that of the eucalypt forest. Because of the enhanced dry-season availability of water in the Melaleuca forest and its larger LAI, average annual water use of the Melaleuca forest was almost 60% larger than that of the eucalypt forest. Despite differences in Q l, Q s and annual water use between forests, the ratio of LAI to stand water use was similar for all seasons in both forests. The applicability of ‘universal rules’ linking tree water use and tree hydraulics and the importance of ecosystem location on site water budgets and plant adaptations are discussed.

Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions.

We studied the seasonal patterns of water use in three woody species co-occurring in a holm oak forest in northeastern Spain. The three species studied, Quercus ilex L., Phillyrea latifolia L. and Arbutus unedo L., constitute more than 99% of the total basal area of the forest. The study period included the dry seasons of 1999 and 2000. Water use was estimated with Granier-type sap flux sensors. Standard meteorological variables, soil water content and leaf water potentials were also monitored. All monitored individuals reduced leaf-related sap flow (Q(l)) during the summer, concurrent with an increase in soil moisture deficit (SMD). Despite similar maximum Q(l) between species, the decline in Q(l) with increasing SMD was species-dependent. The average reduction in Q(l) between early summer and the peak of the drought was 74% for A. unedo (n = 3), 58% for P. latifolia (n = 3) and 87% for Q. ilex (n = 1). The relationship between canopy stomatal conductance (G(s)) and vapor pressure deficit (D) changed during the course of the drought, with progressively lower G(s) for any given D. Summertime reductions of Q(l) and G(s) were associated with between-species differences in vulnerability to xylem embolism, and with the corresponding degree of native embolism (lowest in P. latifolia and highest in Q. ilex). Our results, combined with previous studies in the same area, outlined differences among the species studied in manner of responding to water shortage, with P. latifolia able to maintain water transport at much lower water potentials than the other two species. In an accompanying experiment, A. unedo responded to an experimental reduction in water availability by reducing Q(l) during the summer. This species also modified its water use between years according to the different seasonal patterns of precipitation. These results are discussed in relation to the possible impacts that climate change will have on Q. ilex-dominated forests.

A model of canopy photosynthesis and water use incorporating a mechanistic formulation of leaf CO 2 exchange

A model of the carbon uptake and water balance of forest stands is described where leaf photosynthesis is represented by a mechanistic model of photosynthesis by C 3 plants. Data are presented to support an empirical relationship linking stomatal conductance, photosynthesis, relative humidity and ambient CO 2 concentration. The model was applied to stands of Pinus radiata subject to extremes of water and nutrient availability. Simulated water storage in the root zone agreed with measurements conducted over a 5 year period. Simulated and measured seasonal patterns of water use reached maximum rates of approximately 7 mm day −1 in summer for irrigated stands with projected leaf area indices of approximately 8. Simulated annual net photosynthesis (net of photorespiration and day-time foliar respiration) ranged from approximately 17 Mg C ha −1 year −1 for control stands to approximately 45 Mg C ha −1 year −1 for irrigated and fertilised stands.

Leaf conductance and transpiration, and water relations of evergreen and deciduous perennials co‐occurring in a moist chaparral site

Abstract. Diurnal courses of leaf conductance, water potential and environmental parameters were measured through the year. The seasonal decreases in plant water potentials were greatest in evergreen H. arbutifolia, intermediate in winter deciduous C. occidentalis and least in drought deciduous A. californica. The seasonal patterns of water use were very similar. Estimates of soil root‐stem conductances to liquid water flux indicate that during the spring, conductances are high, that during the early summer there is a daily shift from high morning conductances to lower afternoon conductances, and that late summer conductances are low.

Deep drainage and water use of forests and pastures grown on deep sands in a Mediterranean environment

The neutron scattering technique was used to measure soil-moisture storage beneath native hardwood forests, plantations of softwood forests, perennial pastures and winter annual pastures growing in deep sands of the southwest of Western Australia. The seasonal patterns of water use and of deep drainage to groundwater were calculated using measured soil-moisture characteristics. Fourteen-year-old Pinus pinaster (Ait.) plantations, containing ∼1200 trees per hectare, transpired more water than the native forest they replaced. The pines depleted the soil water faster, and to a greater degree. Deep drainage beyond 6 m was much less in the soil below the pine plantations, indicating a decrease in recharge of shallow groundwaters. The perennial pastures showed a pattern of water use, soil-water depletion and deep drainage similar to the native forests. The winter annual pastures, however, used less water than the native forest, and deep drainage was increased.