Tropical wetlands for climate change research, water quality management and conservation education on a university campus in Costa Rica

EARTH University is a small agronomic university with a theme of sustainability in eastern Costa Rica. Several natural and constructed wetlands on its campus are used for research, water quality improvement, and higher education. It has become an important location for research and teaching on humid tropical wetland ecology and management. A 112-ha flow-through Raphia taedigera (Arecaceae) forested wetland is being used for climate change research, focusing on carbon sequestration and methane generation. Methane emissions are measured seasonally and are comparable to rates in tropical wetlands published elsewhere. Carbon sequestration by the wetland appears to be substantially higher than similar flow-through temperate zone wetlands. Treatment wetlands are used on campus to improve water quality of effluents from an animal farm, a dairy plant, a landfill, and a banana paper plant. Water quality was substantially improved in all of these wetlands except the landfill leachate wetland. All of these campus wetlands have been integrated into the four-year education program of EARTH University and 22 undergraduate projects have been completed on wetlands over the past 14 years.     

Non-thiol farnesyltransferase inhibitors: N-(4-tolylacetylamino-3-benzoylphenyl)-3-arylfurylacrylic acid amides

We have designed arylfurylacryl-substituted benzophenones as non-thiol farnesyltransferase inhibitors utilizing a novel aryl binding site of farnesyltransferase. These compounds display activity in the low nanomolar range.     

Is peat accumulation in mangrove swamps influenced by the “enzymic latch” mechanism?

Mangrove swamps accumulate a significant amount (45–98 %) of organic carbon in sediments; however, there is a knowledge gap in explaining the mechanism behind this. Through the analysis of substrate samples from a red mangrove (Rhizophora mangle) swamp in southwest Florida, USA, this study investigated whether the “enzymic latch”, which suppresses decomposition in northern peatlands, is prevalent in mangrove soils. Laboratory analyses were performed to investigate the four hypotheses of the “enzymic latch”. Results showed that under aerobic conditions mangroves soil samples have significantly higher phenol oxidase activity (two-fold, p < 0.05), but lower phosphatase activity (?33 %, p < 0.05), β-glucosidase activity (?14 %) and glucosaminidase activity (?11 %) compared to anaerobic conditions. Soil samples supplemented with phenol oxidase showed significantly lower phenolic concentration (?8.3 %, p < 0.01), but increased β-glucosidase (+79 %, p < 0.05), xylosidase (+99 %, p < 0.01) and glucosaminidase (+102 %, p < 0.01) activities. Supplementation of lignin-based solution significantly lowered β-glucosidase (?55 %, p < 0.001), sulphatase (?82 %, p < 0.001) and glucosaminidase (?45 %, p < 0.01) activities. Based on these findings, it is concluded that the “enzymic latch” is highly likely to play a key role in suppressing decomposition rates in red mangrove covered areas of mangrove swamps.     

Ecological engineering strategies to reduce flooding damage to wetland crops in central China

Ecological engineering techniques are widely used in Chinese agriculture to reduce wastes and improve efficiency, but rarely to address crop loss associated with flooding. In the middle Yangtze River basin in central China, dish-shaped areas that formerly contained shallow lakes and marshes are now empoldered for the cultivation of rice, fish and other crops. These areas are economically productive but regularly experience crop damage due to rainfall amounts exceeding the removal capacity of pumps and drainage canals. A field investigation gathered existing data on landforms, hydrology, agricultural and aquacultural practices, and recent flooding events at two scales: Xiaogang Farm, 24 km², and Honghu Flood Diversion Area, 2800 km². Computer simulations suggested that local-scale increases in pumping capacity would effectively reduce local flooding damage, but this approach would be less effective if implemented over a wide area. Proposed ecological engineering strategies for flood resistance, including converting some low-position area from rice to flood-tolerant crops such as lotus (Nelumbo nucifera) or wild rice stem (Zizania latifolia), and raising dikes around the converted fields to allow passive storage of excess water during heavy rains, may reduce damage at both local and wide scales.     

Characterization of two members of a novel malic enzyme class.

The Gram-negative bacterium Rhizobium meliloti contains two distinct malic enzymes. We report the purification of the two isozymes to homogeneity, and their in vitro characterization. Both enzymes exhibit unusually high subunit molecular weights of about 82 kDa. The NAD(P)(+) specific malic enzyme [EC 1.1.1.39] exhibits positive co-operativity with respect to malate, but Michaelis-Menten type behavior with respect to the co-factors NAD(+) or NADP(+). The enzyme is subject to substrate inhibition, and shows allosteric regulation by acetyl-CoA, an effect that has so far only been described for some NADP(+) dependent malic enzymes. Its activity is positively regulated by succinate and fumarate. In contrast to the NAD(P)(+) specific malic enzyme, the NADP(+) dependent malic enzyme [EC 1.1.1.40] shows Michaelis-Menten type behavior with respect to malate and NADP(+). Apart from product inhibition, the enzyme is not subjected to any regulatory mechanism. Neither reductive carboxylation of pyruvate, nor decarboxylation of oxaloacetate, could be detected for either malic enzyme. Our characterization of the two R. meliloti malic enzymes therefore suggests a number of features uncharacteristic for malic enzymes described so far.     

Methane emissions from freshwater riverine wetlands

To better understand methane emissions from freshwater riverine wetlands, seasonal and spatial patterns of methane emissions were measured over a 1-year period from created freshwater marshes and a river division oxbow, and at a river-floodplain edge (riverside) in central Ohio, USA. Plots were distributed from inflow to outflow and from shallow transition edges to deep water zones in the marshes and oxbow. Median values of CH₄ emissions ranged from 0.33 to 85.7 mg-CH₄-C m⁻² h⁻¹, at the riverside sites and 0.02-20.5 mg CH₄-C m⁻² h⁻¹ in the created marshes. The naturally colonizing marsh had more methane emissions (p = 0.047) than did the planted marsh, probably due to a history of higher net primary productivity in the former. A significant dry period and lower productivity in the oxbow may explain its low range of methane emissions of −0.04 to 0.09 mg CH₄-C m⁻² h⁻¹. There were significantly higher rates of methane emissions in deep water zones compared to transition zones in the created marshes. Overall CH₄ emissions had significant relationships with organic carbon and soil temperature and appear to depend on the hydroperiod and vegetation development. Riparian wetlands can be designed to minimize greenhouse gas emissions while providing other ecosystem services.     

Malic enzyme cofactor and domain requirements for symbiotic N2 fixation by Sinorhizobium meliloti

The NAD(+)-dependent malic enzyme (DME) and the NADP(+)-dependent malic enzyme (TME) of Sinorhizobium meliloti are representatives of a distinct class of malic enzymes that contain a 440-amino-acid N-terminal region homologous to other malic enzymes and a 330-amino-acid C-terminal region with similarity to phosphotransacetylase enzymes (PTA). We have shown previously that dme mutants of S. meliloti fail to fix N(2) (Fix(-)) in alfalfa root nodules, whereas tme mutants are unimpaired in their N(2)-fixing ability (Fix(+)). Here we report that the amount of DME protein in bacteroids is 10 times greater than that of TME. We therefore investigated whether increased TME activity in nodules would allow TME to function in place of DME. The tme gene was placed under the control of the dme promoter, and despite elevated levels of TME within bacteroids, no symbiotic nitrogen fixation occurred in dme mutant strains. Conversely, expression of dme from the tme promoter resulted in a large reduction in DME activity and symbiotic N(2) fixation. Hence, TME cannot replace the symbiotic requirement for DME. In further experiments we investigated the DME PTA-like domain and showed that it is not required for N(2) fixation. Thus, expression of a DME C-terminal deletion derivative or the Escherichia coli NAD(+)-dependent malic enzyme (sfcA), both of which lack the PTA-like region, restored wild-type N(2) fixation to a dme mutant. Our results have defined the symbiotic requirements for malic enzyme and raise the possibility that a constant high ratio of NADPH + H(+) to NADP in nitrogen-fixing bacteroids prevents TME from functioning in N(2)-fixing bacteroids.     

Book reviews

Wetlands have been widely applied for water quality amelioration. Enzymatic analysis was applied in a study of decomposition in constructed wetlands. We hypothesise that soil enzyme activities would be lower in wetland sediment than adjacent upland and that the lower soil enzyme activities are partly responsible for the water quality amelioration. Four soil enzyme activities (β-glucosidase, β-N-acetylglucosaminidase, phosphatase, and arylsulfatase) and microbial activity (electron transport system activity) were measured across a transect from a upland soil to a wetland sediment in two constructed wetland sites in the USA. Along with the activities, hydrochemistry was determined in inflow and outflow of the wetlands. In both wetlands, the enzyme activities in the sediments were significantly lower than the adjacent upland soils. For hydrochemistry, significant decreases were observed in phosphate and nitrate concentrations in outflow water compared to inflow water. However, there were no significant changes in other anions (F^-, Cl^-, SO ₄ ^2- . For dissolved organic carbon, it seems that the wetlands would be a source rather than a sink. The results suggest that the enzymatic approach represents a valuable method to assess decomposition processes in wetland sediments, and that characteristically low enzyme activities in the sediments may be important in the water quality amelioration function. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wetland Restoration at a Former Nike Missile Base in the Great Lakes Basin

Restoration of an abandoned 16-ha Nike missile base site located on a former wetland in the lower Detroit River (Michigan, U.S.A.) was investigated with an emphasis on wetland restoration. The site included a 2.7-ha abandoned missile base, a 1.3-ha lake, 10.4 ha of emergent and submersed wetlands, and 1.8 ha of uplands. Aquatic beds in the shallow bay connected to the river supported floating leaved and submersed aquatics including Nymphaea tiiberosa, Vallisneria antericana, Elodea canadensis, and Heteranthera dubia, with mats of green, filamentous algae. A 10-ha diked wetland adjacent to the site was dominated by Typha spp., Salix spp., Nymphaea tuberosa, Myriophyllum spicatum, Elodea canadensis, Chara sp., and Juncus effusus. Restoration objectives included a nature preserve, an outdoor recreation area, an experimental wetland complex, and an environmental education center. Ten alternative designs were suggested, including four with wetlands open to the bay, three with diked wetlands, and the rest involving island construction, a reconstructed upland site, or a wetland research facility. Alternatives were evaluated for their contribution to local ecology, research, education and wildlife, ease of maintenance, and probability of success. Construction of a wetland resembling conditions before construction of the base was recommended for its low maintenance and opportunity for research on non diked wetland design and construction in protected bays in the Laurentian Great Lakes. Recreational and educational opportunities were also recommended as part of the site restoration.     

A first generation ecosystem model of the Des Plaines River experimental wetlands

A first generation wetland ecosystem model is developed from first-year field data for four constructed freshwater marshes at the Des Plaines River Wetland Demonstration Project in northeastern Illiois, USA. The model, which includes hydrology, sediment and phophorus algorithms common for all four wetlands, was used for the integration of data collected as part of the many different aspects of the demonstration project and for prediction of wetland function under varying hydrologic and chemical loadings. Stepwise calibration was completed on the model for the hydrology, sediment, productivity, and phosphorus submodels. Separate sedimentation coefficients were necessary for each wetland land and each season. Preliminary simulations investigate the role of changing flow conditions in the wetlands on phosphorus retention. As simulated inflow increased from 34 to 136 cm/wk, phosphorus retention increased from 1.5 to 3.3 g P m⁻² yr⁻¹ while retention efficiency decreased from 67 to 37%.