Metabolism of a tropical rainforest stream

Gradients in photosynthesis (P) and respiration (R) were measured on an unperturbed portion of the Rio Mameyes, a tropical stream in the Luquillo Experimental Forest, northeastern Puerto Rico. Rates of P, which were similar to those of streams in temperate-deciduous forests, were low in the heavily canopied headwaters (\u3c70 g O2 m−2 y−1) and were higher (453–634 g O2 m−2 y−1) in middle and lower reaches. Periphyton biomass did not show the expected increase as the canopy opened downstream, probably because of increasing herbivory in downstream reaches. Rates of R, which were much higher than in most temperate streams, also were lower in the headwaters (767 g O2 m−2 y−1) than in the middle and lower reaches (1550–1660 g O2 m−2 y−1). High rates of R and suppressed periphyton abundance caused annual P/R to be \u3c\u3c1 from headwaters to lower reaches. Results for the Rio Mameyes suggest that intense herbivory, which is favored by the presence of large herbivores and consistently high temperatures, may be more typical of tropical than temperate streams. Results also show that the tropical rainforest provides the stream with sufficient amounts of labile organic C to support high rates of respiration over long distances across the basin

Limnological Response of Las Curias Reservoir, San Juan, Puerto Rico: Successful Management of the Invasive Aquatic Fern, <i>Salvinia molesta</i>

The anthropogenic deterioration of aquatic ecosystems affects water resources due to agricultural malpractices, pollution from domestic septic tanks, recreational activities, and poor watershed management, among other factors. This study examines the management of Las Curias Reservoir, San Juan, Puerto Rico, after the 2016 arrival of the invasive aquatic fern Salvinia molesta. In September 2019, a community-led initiative introduced the Cyrtobagous salviniae weevil, an effective biological control agent for S. molesta, and commenced a mechanical removal campaign using an aquatic harvester. Limnological sampling (September 2019 to September 2022) and drone flights were employed to measure physicochemical and floating plant cover changes, respectively, in the reservoir. Monitoring of weevils in the reservoir demonstrated rapid establishment and dispersal, which resulted in visible damage including browning of plants and eventually sinking of entire mats. From 23 July 2019, the reservoir surface was predominantly covered by salvinia, occupying an area of 17.7 ha (100% coverage). This coverage decreased to 12.6 ha (71%) by 29 January 2021. By 12 August 2022, the coverage had been substantially reduced to just 1.1 ha, representing only 6% of the reservoir surface. In 2022, the reservoir recorded an average dissolved oxygen concentration of 2.4 mg L−1 (±0.0, n = 144), the highest in the study period and indicative of ecosystem recovery. After three years of control efforts, dissolved oxygen, pH, and specific conductance returned to levels recorded prior to Salvinia molesta introduction. This ecosystem recovery, a first in Puerto Rico, could be attributed to early use of mechanical control and the long-term impact of biological control

Sources of reactive nitrogen affecting ecosystems in Latin America and the Caribbean: current trends and future perspectives

While the amount of reactive nitrogen circulating at the global level has increased markedly in the last century, the effects of this increase are largely seen at the regional level due to interacting ecological and socio-economic factors. In contrast with most other regions of the world, Latin America and the Caribbean (LA-Ca) stand out due to the fact that the major input of reactive nitrogen (Nr) still occurs naturally via biological nitrogen fixation (BNF) in natural ecosystems as opposed to anthropogenic inputs of synthetic fertilizer, fossil fuel combustion and cropping with leguminous species. Largely due to economic reasons, the consumption of fertilizer N in the LA-Ca region is still low in comparison with the average consumption of the world. However, the fertilizer N consumption is increasing at a much faster rate than that in developed regions of the world, like USA and Canada. The Nr production through BNF in cultivated plants that fix nitrogen (C-BNF) is 5 times lower than that occurring naturally in Latin America, but is still equivalent to 16% of the world C-BNF. The cultivation of nitrogen-fixing crop species in the LA-Ca region is also increasing, almost entirely due to the expansion of soybean fields in the central and northern regions of Brazil and the Pampa region of Argentina. Other anthropogenic activities in the region that contribute to an increase in the circulation of reactive nitrogen include the impact of biomass burning and urbanization. In the last decade, an average of 47,000 km 2 per year of forests was burned in the LA-Ca region. The environmental impact of urban centers in the LA-Ca region has become very important, since an intense urbanization process is occurring in this region, at an intensity that far exceeds urban development in the northern hemisphere. The consequences of increased urbanization include increased emissions of NO x to the atmosphere due to the fossil fuel combustion, and the lack of sewage treatment facilities in most cities of the LA-Ca result in a large volume of untreated sewage discharged into surface waters, creating serious environmental problems. The combination of rapid urbanization and agricultural intensification in this region suggest that concern is warranted for the potential for increase in the circulation of reactive nitrogen in the very near future. At the same time, the opportunity still exists to mitigate some of the consequences of human impact on the nitrogen cycle in a region that still maintains a large fraction of its natural ecosystems intact.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46029/1/10533_2006_Article_9000.pd