Variation of stream metabolism along a tropical environmental gradient

Stream metabolism is affected by both natural and human-induced processes. While metabolism has multiple implications for ecological processes, relatively little is known about how metabolic rates are influenced by land use in tropical streams. In this study, we assessed the metabolic characteristics and related environmental factors of six streams located in a transition area from Cerrado to Atlantic Forest (São Carlos/Brazil). Three streams were relatively preserved, while three were flowing through more agriculturally and/or urban impacted watersheds. Surface water samples were analyzed for biological and physico-chemical parameters as well as discharge and percentage of canopy cover. Metabolism was determined through the single-station method to estimate gross primary production (GPP), ecosystem respiration (ER) and net ecosystem production (NEP) with BAyesian Single-station Estimation (BASE). Nutrient concentrations tended to be higher in impacted versus preserved streams (e.g., average total phosphorus between 0.028-0.042 mg L-1 and 0.009-0.038 mg L-1, respectively). Average canopy cover varied between 58 and 77%, with no significant spatial or seasonal variation. All streams were net heterotrophic (ER exceeded GPP) in all sampling periods. GPP rates were always lower than 0.7 gO2 m-2 d-1 in all streams and ER varied from 0.6 to 42.1 gO2 m-2 d-1.  Linear Mixed-Effect models showed that depth, discharge, velocity and total phosphorus are the most important predictors for GPP. For ER, depth, velocity and canopy cover are significant potential predictors. Canopy cover was the main light limiting factor and influenced stream metabolism. Our findings reinforced the concepts that shifts in the shading effect provided by vegetation (e.g., through deforestation) or changes in discharge (e.g., through land use conversion or water abstractions) can impact freshwater metabolism. Our study suggests that human activities in low latitude areas can alter tropical streams’ water quality, ecosystem function, and the degree of riparian influence. Our data showed that tropical streams can be especially responsive to increases of organic matter inputs leading to high respiration rates and net heterotrophy, and this should be considered to support management and restoration efforts

Environmental factors and thresholds for nitrogen fixation by phytoplankton in tropical reservoirs

In theory, the phytoplankton community of freshwater ecosystems with low concentrations of dissolved inorganic nitrogen (DIN) can obtain this element by atmospheric nitrogen (N2) fixation. This process could explain the dominance of cyanobacteria in tropical reservoirs, yet is rarely quantified in these systems. Assessing the factors related to N2 fixation can assist in the management of cyanobacterial blooms. Our study characterized environmental factors related to N2 fixation in Brazilian tropical reservoirs with contrasting trophic states, and defined quantitative thresholds for water chemistry and physical characteristics that stimulated N2 fixation. We used field assays with 15N for estimating N2 fixation rates by phytoplankton. The highest rates normalized by chlorophyll-a (maximum of 143 × 10−4 μg-N μg-Chl-a−1 h−1) coincided with eutrophic conditions and presence of diazotrophs. Receiver operating characteristic (ROC) analysis provided significant thresholds for water temperature (≥22°C), soluble reactive phosphorus (SRP) (≥3.0 μg-P L−1), total phosphorus (TP) (≥20.5 μg-P L−1), DIN:SRP (≤487) and DIN:TP (≤82) molar ratios, chlorophyll-a (≥12 μg L−1), and total suspended solids (≥4 mg L−1). Censored regressions confirmed that temperature, chlorophyll-a, and phosphorus were important predictors of N2 fixation rates. In general, the N2 fixation rates determined in this study were lower than those found for temperate reservoirs. However, the temperature threshold of 22°C or above, identified in our analysis, suggests that phytoplankton have the potential to fix N2 throughout the year in tropical reservoirs. Our results suggested that phosphorus is the main nutrient controlling the rates of N2 fixation when N2-fixing cyanobacteria were present. Phosphorus abatement is, thus, crucial for managing the trophic state and controlling N2-fixing cyanobacteria in these ecosystems

Citizen science participation in research in the environmental sciences: key factors related to projects’ success and longevity

ABSTRACT The potential impacts of citizen science initiatives are increasing across the globe, albeit in an imbalanced manner. In general, there is a strong element of trial and error in most projects, and the comparison of best practices and project structure between different initiatives remains difficult. In Brazil, the participation of volunteers in environmental research is limited. Identifying the factors related to citizen science projects’ success and longevity within a global perspective can contribute for consolidating such practices in the country. In this study, we explore past and present projects, including a case study in Brazil, to identify the spatial and temporal trends of citizen science programs as well as their best practices and challenges. We performed a bibliographic search using Google Scholar and considered results from 2005-2014. Although these results are subjective due to the Google Scholar’s algorithm and ranking criteria, we highlighted factors to compare projects across geographical and disciplinary areas and identified key matches between project proponents and participants, project goals and local priorities, participant profiles and engagement, scientific methods and funding. This approach is a useful starting point for future citizen science projects, allowing for a systematic analysis of potential inconsistencies and shortcomings in this emerging field

Citizen science participation in research in the environmental sciences: key factors related to projects’ success and longevity

<div><p>ABSTRACT The potential impacts of citizen science initiatives are increasing across the globe, albeit in an imbalanced manner. In general, there is a strong element of trial and error in most projects, and the comparison of best practices and project structure between different initiatives remains difficult. In Brazil, the participation of volunteers in environmental research is limited. Identifying the factors related to citizen science projects’ success and longevity within a global perspective can contribute for consolidating such practices in the country. In this study, we explore past and present projects, including a case study in Brazil, to identify the spatial and temporal trends of citizen science programs as well as their best practices and challenges. We performed a bibliographic search using Google Scholar and considered results from 2005-2014. Although these results are subjective due to the Google Scholar’s algorithm and ranking criteria, we highlighted factors to compare projects across geographical and disciplinary areas and identified key matches between project proponents and participants, project goals and local priorities, participant profiles and engagement, scientific methods and funding. This approach is a useful starting point for future citizen science projects, allowing for a systematic analysis of potential inconsistencies and shortcomings in this emerging field.</p></div

Patterns of macroinvertebrate production and energy flow in headwater streams of the Brazilian Savanna

Secondary production estimates are an important element of ecosystem ecology because they facilitate quantification of the roles of consumers in material and energy cycling. We estimated production and resource consumption of stream macroinvertebrates, along with stream metabolism and organic matter storage in 3 relatively undisturbed Savanna headwater streams in southeastern Brazil. We measured production of benthic macroinvertebrates and reach-scale metabolism from October 2015 to September 2016. Mean annual values of gross primary production and ecosystem respiration varied from 0.06 to 0.22 and 3.96 to 23.76 g O2 m−2 d−1, respectively, reflecting net heterotrophic conditions. Total secondary production ranged from 11.0 to 13.5 g ash-free dry mass m−2 y−1. Gatherers, shredders, and predators were the most important contributors to production, ranging from 11 to 30%, 21 to 39%, and 20 to 49% of total production, respectively, and detrital pathways accounted for most energy flow. Shredders only ingested 3.4 to 8.1% of total available food resources, suggesting that food resource availability does not limit production in these streams. To our knowledge, this study provides the first quantification of energy flow patterns in Brazilian Savanna streams using secondary production estimates and is one of the few measuring growth rates and secondary production of macroinvertebrates with short generation times under field conditions in tropical streams. Furthermore, this study is one of the few to link stream metabolism and organic matter storage to secondary production. Our results will help to understand reference conditions in the poorly studied streams of a region particularly threatened by human activities and potentially elsewhere in tropical systems