Summer Water Table Research Articles

Sugarcane Cultivar Response to High Summer Water Tables in the Everglades

Sugarcane (interspecific hybrids of Saccharum spp.) in the Everglades Agricultural Area (EAA) in Florida is frequently subjected to periods of higher‐than‐desired water levels. This study was conducted to evaluate yields of nine sugarcane cultivars subjected to two higher‐than‐conventional water tables in the EAA during the summer rainy season from the plant cane through the second‐ratoon annual crop cycles. Field experiments were planted in February 1997 and January 1998. During the summers from 1997 through 1999, we sought to maintain water <15 cm below the soil surface (BSS) in the wetter field and from 15 to 38 cm BSS in the drier field. Water tables for sugarcane in the EAA fluctuate from 40 to 95 cm BSS. Targeted water levels were achieved for 40 d in 1997, 104 d in 1998, and 96 d in 1999 in the wetter field and for 35 d in 1997, 96 d in 1998, and 82 d in 1999 in the drier field. The mean sugar per hectare in the wetter field was 91.7% that of the drier field. Yields of ‘Canal Point (CP) 72–2086’ and ‘CP 82–1172’ were not affected by water table. Cultivar CP 85–1308 had higher yields in the wetter field in two of five harvests. Sugar per hectare of ‘CP 80–1743’ was reduced by 25.1% in the wetter field. The variability among commercial cultivars to maintain yields at high water tables suggests that routine screening of promising sugarcane genotypes under high water tables would help identify more cultivars that maintain high yields in wetter conditions in the EAA.

Sugarcane Cultivar Response to High Summer Water Tables in the Everglades

Sugarcane Cultivar Response to High Summer Water Tables in the Everglades

Hydrological processes in a Cirsio-Molinietum fen meadow: Implications for restoration

Cirsio-Molinietum fen meadows are seriously threatened by desiccation, acidification and eutrophication. In a nature reserve, with well-developed fen meadow stands groundwater tables and the chemical composition of groundwater and top soil were measured along a gradient during several years in the 1990s. The reserve consists of a depression, which is surrounded by ridges on all sides. Summer groundwater tables, which are being determined by regional features outside the reserve, drop down at least 1 m below the soil surface, whereas during the winter season a pool is formed. A concentrated flux of base-rich groundwater is brought up at the margin of the (eastern) exfiltration part of the pool, where downstream infiltration takes place. These processes, which cause a whole variety in site conditions, and consequently also in plant communities, are phenomena of a local groundwater system. An essential prerequisite for the functioning of such a groundwater system is the presence of pools during the winter season. When summer groundwater tables, which determine the origin and the extension of pools, are too low, measures outside nature reserves have to be taken to restore high summer water tables. Successful restoration of fen meadows requires sod cutting along the entire gradient. Since relatively small height differences can result in groundwater flow, restoring this type of hydrological systems on former agricultural areas requires first of all, restoration of the relief.

ON-FARM MANAGEMENT OF IRRIGATION FOR MAIZE IN EASTERN ONTARIO

A field experiment was conducted in the summer of 1996 to evaluate the supplemental irrigation needs of maize in fields located on sandy soils in eastern Ontario. Field and laboratory measurements of soil properties were made. Plow layer and deficit irrigation management approaches were evaluated. The plow layer soil depth was considered to be 300 mm, and for deficit irrigation management a soil depth of 400 mm was used. Irrigation requirements using rain and evapotranspiration data of the humid summer of 1996, as well as the drier summer of 1974, were evaluated. The results show that using a 400 mm root zone depth and 25 mm of water per irrigation led to less water losses by drainage, lower irrigation water requirements and fewer irrigations as compared to using a 300 mm root zone depth. Wilting began at 60% soil moisture depletion, thus it is suggested that irrigation begin at 50% moisture depletion to avoid costly crop stress. The principal assumptions for irrigation scheduling were that the soil is at field capacity at the beginning of June and where the summer water table is deeper than 1.6 m, the upward flux from the water table is negligible.

Methane Emissions from a Gully Mire in Mid-Wales, U.K. under Consecutive Summer Water Table Drawdown

Wetlands are a major contributor to the global methane (CH{sub 4}) budget. Currently there is a consensus view that drought restrains CH{sub 4} emissions from wetlands. However, a 6-year field experiment investigating the effects of persistent summer water table drawdown on a gully mire in mid-Wales, U.K. demonstrated a 2-year boom and bust cycle of CH{sub 4} emissions followed by a recovery during the third year, when compared with emissions from a control wetland in which the water table remained at or above the peat surface. This cyclical trend was subsequently replicated by the control wetland following natural summer drought. The experimental wetland was affected less by this natural drought following previous water table drawdown. Depth profiles of CH{sub 4} production suggested that consecutive water table drawdown resulted in a translocation of peak methanogen activity lower down the peat profile, where emissions were affected less by subsequent drawdown. These findings suggest that wetland CH{sub 4} flux models need to consider the possibility that methane emission-water table relationships are dependent on the pattern and frequency of drought events.

Northern Canadian wetlands: Net ecosystem CO2 exchange and climatic change

Northern Canadian peatlands represent a long term sink for atmospheric carbon dioxide (CO2), however there is concern they may become a net source of CO2 due to climatic change. Climatic change is expected to result in significant changes in regional hydrology in boreal and subarctic regions of Canada. A hydrologic model predicted a summer water table drop of 0.14 m in northern Canadian fens given an increase in summer temperature and rainfall of 3°C and 1 mm d-1, respectively. Moreover, surface peat temperature increased by 2.3°C. Net ecosystem exchange of CO2 was modelled using these modelled hydrologic and thermal changes with respiration:peat temperature and water table:net ecosystem production relationships developed from measurements at wetlands in northern Sweden and near Churchill, Manitoba. Model results indicate that the net atmospheric CO2 sink function of fens may be enhanced under future 2 × CO2 scenarios, while bogs may become a net source of atmospheric CO2. If the net ecosystem productivity response to the new hydrologic conditions was ignored then the model predicts a decrease in summer carbon storage for all peatland types.

Control of Local Nutrient Dynamics in Mires by Regional and Climatic Factors: A Comparison of Dutch and Polish Sites

1 We tested the influence of geographical gradients upon nutrient dynamics in the root environment of the vegetation of mires in north-eastern Poland and the Netherlands. The study areas show differences in the water level fluctuations, and atmospheric nitrogen deposition (the Netherlands, 50kg N ha-1 year-1; Poland, 5 10kg N ha-1 year-1). 2 Nitrogen and phosphorus mineralization, decomposition, denitrification and nitrous oxide emission were studied during 6 weeks in May June and correlated with characteristics of the interstitial water and the soil. Five types of mires (herbaceous bog, forested bog, herbaceous rich-fen, river marginal fen and alder fen forest) were compared. 3 Inorganic N as well as P release were faster in the Dutch than in the Polish mires of the same type. Denitrification and nitrous oxide emission were also faster in the Dutch mires, with the exception of the Polish alder forest, where denitrification was high because of high N richness and a strongly falling water table. 4 Principal component analysis of 18 physical and chemical soil and interstitial water variables resulted in four components: I, 'soil redox status'; II, 'soil base status'; III, 'interstitial water nutrient richness': IV, 'soil P richness'. In multiple regressions, N mineralization correlated positively with component III, P release with components III and IV, and cellulose decomposition with components II and IV. Both denitrification and nitrous oxide emission correlated positively with components I and II. 5 It was concluded that the lower P release rates in the Polish compared to the Dutch mires were due to higher calcium levels and lower summer water tables, which was partly attributed to the Polish continental climate. The higher rates for N mineralization, denitrification, nitrous oxide emission and cellulose decomposition in the Dutch sites were attributed to the high N deposition in the Netherlands.

Methane flux from drained northern peatlands: Effect of a persistent water table lowering on flux

Measurements of CH4 flux from drained and undrained sites in three northern Ontario peatlands (a treed fen, a forested bog, and a treed bog) were made from the beginning of May to the end of October 1991. In the drained portions, the water table had been lowered between 0.1 and 0.5 m, compared to the water table of the undrained portion of the peatlands. The mean seasonal CH4 flux from the undrained portions of three peatlands was small, ranging from 0 to 8 mg m−2d−1, but similar to the CH4 flux from other treed and forested northern peatlands. The mean seasonal CH4 flux from the drained portion of the peatlands was either near zero or slightly negative (i.e.,uptake): fluxes ranged from 0.1 to −0.4 mg m−2 d−1. Profiles of CH4 in the air‐filled pores in the unsaturated zone, and the water‐filled pores of the saturated zone of the peat at the undrained sites, showed that all the CH4 produced at depth was consumed within 0.2 m of the water table and that atmospheric CH4 was consumed in the upper 0.15 m of the peatland. On the basis of laboratory incubations of peat slurries to determine CH4 production and consumption potentials, the lowering of the water table eliminated the near‐surface zone of CH4 production that existed in the undrained peatland. However, drainage did not alter significantly the potential for CH4 oxidation between the water table and peatland surface but increased the thickness of the layer over which CH4 oxidation could take place. These changes occurred with a drop in the mean summer water table of only 0.1 m (from −0.2 to −0.3 m) suggesting that only a small negative change in soil moisture would be required to significantly reduce CH4 flux from northern peatlands.

Hydrology and nutrient gradients in North Carolina peatlands

Soil chemistry and hydrology gradients are closely associated with and have often been cited as the causative agents for changes in wetland plant community composition. We analyzed the biogeochemistry and hydrology of three freshwater peatland communities on the North Carolina Coastal Plain—short pocosins, tall pocosins, and gum swamps. We compare this community gradient to the classical bog-fen gradient of northern peatlands. Short pocosins, in the ombrotrophic center of the raised bog complex, have the highest summer water table, with a large part of the peat profile remaining anaerobic throughout the year. They are highly nutrient-deficient with low levels of total and extractable P, N, and basic cations. They additionally have the greatest peat depth, with an organic matter content of ca. 95%. Tall pocosins have a highly seasonal water table, shallower peat depth, low soil nutrient levels, and an average soil organic matter content from 76 to 93% in the top 30 cm. Gum swamp forests have a highly seasonal water table and the shallowest peat depth. They are the most minerotrophic community, based on low organic matter and high N and P content of the soil, but have low levels of exchangeable Ca and Mg and low percent base saturation. All communities had low soil pH (<4). Short pocosins and tall pocosins were effectively differentiated by seasonal hydrology and peat depth but not by soil characteristics, while the pocosins and swamp forest had large differences in seasonal hydrology, peat depth, percent organic matter, and soil nutrients.

Nature management experiments in a derelict reedmarsh. I: Effects of winter cutting

Lowering of the summer water table, eutrophication and dereliction have caused severe ruderalisation of the reedmarsh in the important Belgian wetland site of the Blankaart. The reed vegetation has become totally overgrown by competitive species such as Urtica dioica, Calystegia sepium and Calamagrostis canescens. Management experiments conducted from 1978 to 1986 have shown that a regime of annual winter cutting can substantially reduce the ruderal and nitrophilous character of the vegetation and increase species diversity. The process is mostly linked to the correlated effects of litter removal. The changes in the vegetation are influenced by the position in the zonation/succession. It is argued that, for complete restoration of the vegetation, efforts should be made to raise the summer water table and to stop eutrophication and silting of the pond.

Nature management experiments in a derelict reedmarsh. II: Effects of summer mowing

Lowering of the summer water table, eutrophication and dereliction have caused severe ruderalisation of the marsh vegetation of the Belgian wetland site, The Blankaart. Management experiments, based on an annual summer mowing regime, have shown that the ruderalised mixed-fen vegetation with dominance of competitive species such as Calamagrostis canescens and Glyceria maxima, which has completely lost its reedland character, can develop into a more diverse hayfield vegetation. However, the high nutrient status of the marsh and difficulties with the invasion of seed of hayfield species, due to the changed environment, discourages further distinct changes of the vegetation.

Vegetation and habitat conditions in Western Head Bog, a southern Nova Scotian plateau bog

The southernmost plateau bogs in eastern North America are found in southern Nova Scotia. They are characterized by an extremely wet plateau with high conical hummocks, a partly forested bog slope, and several disjunct species of the Coastal Plain flora.Prevailing water levels on the plateau are high and fluctuate little. They do not start to drop until very close to the plateau margin, and are lowest on the forested parts of the slope. The lagg is wet and has the most strongly fluctuating water levels.Water table location, and thus microtopography of the surface, controls the vegetation pattern of the plateau. A Gaylussacia baccata dwarf shrub heath occupies hummocks 25 cm or more above the 50% summer water table. Utricularia mud bottoms are regularly flooded in summer and the water table never drops more than 5 cm below the surface. The two Scirpus lawn communities occupy an intermediate position.A complex gradient, involving both water level and nutrient regime, controls vegetation changes from the center to the bog border. The bog slope, especially under the forest, is enriched by the detritus cycle. Floristic changes in the vegetation indicate an enrichment of the plateau margin, and possibly also the slope, by drainage water seeping from the plateau. Peat analyses failed to confirm this. Within the lagg, differences in minerotrophy separate the two fen communities, but floristic changes on the hummocks are caused by differences in water table location, nutrient supply, and shading.These plateau bogs are distinguished clearly from those along the west side of the Bay of Fundy by the dominance of mud bottoms rather than lawn communities on the plateau, by the occurrence of many nutrient-demanding species in the ombrotrophic vegetation, and by the presence of Coastal Plain disjuncts, such as Ilex glabra.