Reactive Phosphate Research Articles

Phosphorus Sources and Rates Associated with Nitrogen Fertilization in Mombasa Grass Yield

ABSTRACTNitrogen (N) and phosphorus (P) deficiency is one of the important causes of degradation of cultivated pasture under tropical conditions. The aim of this study was to evaluate phosphate rates and sources, and N rates on the concentration and uptake of N and P, and shoot dry mass (SDM) yield of Megathyrsus maximum grass cv Mombasa in an Ultisol. The trial was carried out in a greenhouse in pots with 4.0 dm−3 of soil. The experiment was arranged in a completely randomized design with four replicates. The 3 × 3 × 3 factorial treatments consisted of phosphorus sources [reactive rock phosphate from Morocco (RPM), reactive rock phosphate from Algeria (RPA) and triple superphosphate (TSP)], three phosphorus rates (0, 150, and 300 mg kg−1), and three N rates (0, 250, and 500 mg kg−1). The SDM and tillering of Mombasa grass were significantly influenced with the TSP, RPM, and RPA application associated with N fertilization. The RPM, RPA, and TSP met the nutritional demands of Mombasa grass. The three P sources showed the same effect on the total N uptake by Mombasa grass. The P use efficiency (PUE) when fertilizer-P sources were added alone by Mombasa grass was <12% of the added P, and PUE decreased as follows: TSP > RPA > RPM. When P and N-fertilizer were added together, the fertilizer-N use efficiency (NUE) was 62%. The reactive phosphate (RPM and RPA) is an efficient P sources for Mombasa grass, but requiring higher rate of application compared to TSP source.

Impact of Treated Sewage Effluent on the Microbiology of a Small Brook Using Flow Cytometry as a Diagnostic Tool

Flow cytometry was applied to assess the microbiological impact of treated sewage effluent discharge into a small brook carrying surface runoff water. Increases in dissolved organic carbon and soluble reactive phosphorous were accompanied by increases in counts of intact bacteria by up to eightfold. Effluent ingress furthermore resulted in a pronounced shift of bacterial clusters. Whereas brook water upstream of the discharge point was characterised by a bacterial cluster with low nucleic acid (LNA) content, downstream water showed a shift to bacteria with high nucleic acid (HNA) content. Changes in the LNA/HNA ratio were largely maintained along the course of the brook. Results suggest that the LNA/HNA ratio can under certain conditions serve as an indicator of anthropogenic nutrient impact. Measuring impact on this low trophic level might be more sensitive and straightforward than measuring macroindicators. More evidence will however be required to assess the usefulness of LNA/HNA measurements to assess the ecological nutrient status of natural waters and the impact of nutrient pollution.

Brachiaria as a Cover Crop to Improve Phosphorus Use Efficiency in a No-till Oxisol

Oxidic soils are phosphorus drains in soil; hence, P availability is a limiting factor in tropical, weathered Oxidic soils. It has been shown that some brachiarias grown as cover crops may increase soil available P to subsequent crops. The objective of this study was to evaluate soil P cycling and availability, as well as the response of soybean to soluble and natural reactive phosphates as affected by ruzi grass (Urochloa ruziziensis, R. Germ. and C.M. Evrard, Crin) grown as a cover crop in a no-till system. Experimental treatments consisted of the presence or absence of ruzi grass in combination with a control (0.0 P) and soluble and reactive rock phosphate broadcast on the soil surface in the winter (80 kg ha-1 P2O5), plus three rates of P applied to soybean furrows (0, 30, and 60 kg ha-1 of P2O5) at planting, in the form of triple superphosphate. Soybean was cropped in two seasons: 2010/2011 and 2011/2012. Soil samples were taken before soybean planting (after desiccation of Brachiaria) at 0.00-0.05 and 0.05-0.10 m for soil available P. Total weight of dry matter and P accumulated in ruzi grass were determined, as well as soybean yields, P in soybean grains, and P use efficiency (PUE). The use of natural phosphate increased soil P availability. The highest yields were obtained with higher application rates of triple superphosphate in the planting furrow combined with broadcast rock phosphate. Broadcast application of Arad reactive phosphate increases and maintains soil available P, and this practice, associated with ruzi grass grown as a cover crop and the use of triple superphosphate applied to soybean furrows, results in higher use of P by soybeans.

Scaling relationships among drivers of aquatic respiration in temperate lakes: from the smallest to the largest freshwater ecosystems

To address how various environmental parameters control or constrain planktonic respiration (PR), we used geometric scaling relationships and established biological scaling laws to derive quantitative predictions for the relationships among key drivers of PR. We then used empirical measurements of PR and environmental (soluble reactive phosphate [SRP], carbon [DOC], chlorophyll a [Chl-a)], and temperature) and landscape parameters (lake area [LA] and watershed area [WA]) from a set of 44 lakes that varied in size and trophic status to test our hypotheses. We found that landscape-level processes affected PR through direct effects on DOC and temperature and indirectly via SRP. In accordance with predictions made from known relationships and scaling laws, scale coefficients (the parameter that describes the shape of a relationship between 2 variables) were found to be negative and have an absolute value <1. Biological parameters scaled positively with physical and chemical processes in accordance with those predicted from theory or previous studies (i.e., temperature >1, others <1). We also found evidence of a significant relationship between temperature and SRP. Because our dataset included measurements of respiration from small pond catchments to the largest body of freshwater on the planet, Lake Superior, these findings should be applicable to controls of PR for the great majority of temperate aquatic ecosystems.

Growth and yield of sugarcane as a function of phosphorus doses and forms of application

ABSTRACT This study aimed to evaluate sugarcane growth and its agricultural and industrial yield influenced by phosphorus (P) sources and forms of application. The experiment was carried out at the Paisa Sugar Mill, in Penedo-AL, Brazil, from February 2012 to February 2013. The adopted experimental design was a randomized block in a factorial arrangement, with four replicates. The treatments consisted of five doses of triple superphosphate applied in the planting furrow (0, 50, 100, 150 and 200 kg ha-1 of P2O5), and three doses of Bayóvar reactive phosphate rock (0, 100 and 200 kg ha-1 of P2O5) applied in the total area. Phosphorus applied in the planting furrow improved sugarcane quality through the reduction of fiber and increases in purity, corrected pol, total recoverable sugar, ton of pol per hectare (TPH) and ton of sugarcane per hectare (TSH). The Bayóvar reactive phosphate rock promoted increases in stem diameter at 120 days after planting (DAP), TPH and TSH. For the interaction triple superphosphate applied in the planting furrow x Bayóvar reactive phosphate rock applied in the total area, there were significant differences in the number of tillers at 30 DAP, stem diameter at 120 DAP and TSH.

Understanding the controls on sediment-P interactions and dynamics along a non-tidal river system in a rural–urban catchment: The River Nene

The release of Phosphorus (P) from river sediments has been identified as a contributing factor to waters failing the criteria for ‘Good Ecological Status’ under the EU Water Framework Directive (WFD). To identify the contribution of sediment-P to river systems, an understanding of the factors that influence its distribution within the entire non-tidal system is required. Thus the aims of this work were to examine the (i) total (PTotal) and labile (PLabile) concentrations in sediment, (ii) the sequestration processes and (iii) the interactions between sediment P and the river water in the six non-tidal water bodies of the River Nene, U.K. Collection of sediments followed a long period of flooding and high stream flow. In each water body, five cores were extracted and homogenised for analysis with an additional core being taken and sampled by depth increments. Comparing the distribution of sediment particle size and PTotal data with soil catchment geochemical survey data, large increases in PTotal were identified in sediments from water body 4–6, where median concentrations of PTotal in the sediment (3603 mg kg−1) were up to double those of the catchment soils. A large proportion of this increase may be related to in-stream sorption of P, particularly from sewage treatment facilities where the catchment becomes more urbanised after water body 3. A linear correlation (r = 0.8) between soluble reactive phosphate (SRP) and Boron in the sampled river waters was found suggesting increased STW input in water bodies 4–6.PLabile concentrations in homogenised cores were up to 100 mg kg−1 PO4–P (generally < 2% of PTotal) and showed a general increase with distance from the headwaters. A general increase in Equilibrium Phosphate Concentrations (EPC0) from an average of 0.9–∼1.7 μm L−1 was found between water bodies 1–3 and 4–6. Fixation within oxalate extractable phases (Al, Fe and Mn) accounted for ∼90% of P binding in water bodies 4–6, but only between 31 and 74% in water bodies 1–3. Statistical models predicting PTotal (R2 = 0.78), oxalate extractable P (R2 = 0.78) and Olsen P (R2 = 0.73) concentrations in river sediments identified Mn oxy-hydroxides (MnOx) as a strong predictive variable along with the location within the river system. It is suggested that MnOx within model predictions is identifying a pool of mixed Fe–Mn oxy-hydroxides (MnOx–FeOOH) or Fe oxy-hydroxide (FeOOH) from the wider FeOxalate pool that are particularly effective at sorbing and fixing P. The findings demonstrate how sediment and P may accumulate along a 100 km non-tidal river system, the extent to which a range of processes can fix P within mineral phases and how natural flooding processes may flush sediment from the river channel. The processes identified in this study are likely to be applicable to similar river systems over their non-tidal water bodies in eastern England.

Scale-dependent environmental control of mesozooplankton community structure in three aquaculture subtropical bays of China

Summary Most subtropical bays of China have been under heavy pollution since the late 1990s, mainly because of the rapid development of aquaculture and discharge of industrial and agricultural wastewater. Some projects were conducted to investigate the zooplankton community in these bays, but those studies were less focused on the relationship between spatial structure of mesozooplankton community and environmental variables in/among bays. The mesozooplankton community structures in relation to physical, chemical and biological variables were studied in three subtropical bays of China with seasons and different spatial scales during 2000 and 2002–2003. Data were collected on temperature (T), salinity (S), concentration of chlorophyll a (Chl a), pH, dissolved oxygen (DO), soluble reactive phosphate (SRP), dissolved inorganic nitrogen (DIN), chemical oxygen demand (COD), suspended particle material (SPM) and mesozooplankton taxonomic abundances. Correlation analysis showed that the main environmental factors correlated to the total abundance of mesozooplankton in these subtropical bays were Chl a, temperature, COD and SRP. Multivariate analysis indicated that DO, Chl a and temperature were the principal factors in influencing spatial differentiation of zooplankton community structure in the inter-bay scale. At the within-bay scale, the influencing factors were different among bays; the main factors were physical variables for Xiangshan Bay and Sanmen Bay, while chemical variables for Yueqing Bay, respectively. The results revealed that the environmental variables that affected spatial structure of mesozooplankton community were different at inter-bay scale and within-bay scales, and zooplankton community was more influenced by chemical (e.g. nutrients/ammonia) variables when under serious eutrophication condition, while it would be more influenced by physical variables (temperature/salinity) when under less eutrophic conditions.

Identifying functional species pool of planktonic protozoa for discriminating water quality status in marine ecosystems

It is cost-effective protocol to identify a functional species pool for marine bioassessment by removing redundant species from a raw dataset. The feasibility of functional species pool for discriminating water quality status was studied based on a dataset of 120 samples of ciliated protozoa. From the full 60-species dataset of the whole ciliate communities, a 35-species subset was identified as a functional species pool, the species number, abundance and biodiversity indices of which were significantly correlated with those of the full species dataset. The spatial pattern of the subset was significantly related to the changes in nutrients soluble reactive phosphates (SRP), nitrate/nitrite nitrogen (NO3-N/NO2-N) and ammonium nitrogen (NH4-N). Four indices of the taxonomic diversity (Δ), taxonomic distinctness (Δ*), average in taxonomic distinctness (Δ+) and the variation in taxonomic distinctness (Λ+) based on this small species pool were significantly correlated with the changes of nutrients NO3-N and/or (NH4-N). The paired indices Δ+ and Λ+ showed a clear decreasing trend of departure from the expected taxonomic pattern. These findings suggest that the 35-species functional species subset may be used as a feasible functional surrogate of ciliated protozoan assemblages for community-based bioassessment in marine ecosystems.

Phosphonium cation-based ionic liquids as neat lubricants: Physicochemical and tribological performance

This paper studies physicochemical properties (density, viscosity, corrosion, thermogravimetry, and conductivity) and tribological behavior of five phosphonium cation-based ionic liquids ([P66614][BEHP], [P66614][C8C8PO2], [P66614][NTf2], [P44414][DBS], and [P4442][DEP]) as neat lubricants within steel–steel contact. A reciprocating ball-on-disc configuration was used to perform tribological tests. Worn surfaces were analyzed by confocal microscopy, SEM, EDS and XPS. Main results showed that: [P66614][NTf2], [P44414][DBS], and [P4442][DEP] showed corrosion activity; the ionic liquids with more reactive phosphate type anion ([P66614][BEHP] and [P4442][DEP]) had the best tribological behavior; the best tribological results were related to the tribofilm formation of two phosphate species.

New insight into the correlations between land use and water quality in a coastal watershed of China: Does point source pollution weaken it?

Uncovering the associations between land use and river water quality is useful for managing land-based pollution in the catchment-coast continuum. However, it is not clear how land use affects water quality in the context of simultaneous point source (PS) pollution. In this study, we develop a self-organizing map (SOM)-based approach to explore the relationship between land use and water quality in the Minjiang River Watershed, Southeast China. Water samples from 139 headwater sub-watersheds were associated with six land use categories, namely, Woodland, Agriculture, Orchard, Built-up, Unused land and Water. Sampling sites are delineated into six clusters based on six water quality parameters: ammonium-N, nitrate-N, total nitrogen, soluble reactive phosphate, total phosphate and potassium permanganate index. Local relationships between land use and water quality among four clusters that have sufficient sample sizes are further identified. There is no significant land use-water quality correlation in one of the four clusters (including 37 sub-watersheds). And the greater the PS pollution is, the less significant the land use-water quality correlations are in clusters. The results demonstrate how PS pollution weakens the land use-water quality correlation. Our method can help to determine whether non-point source or PS pollution exerts greater influence on the quality of the water coming from watershed.

The ability of the DGT soil phosphorus test to predict pasture response in Australian pasture soils – a preliminary assessment

AbstractDiffusive gradients in thin‐films (DGT) technology provides an alternative assessment of available phosphorus (P) for a range of crops, suggesting a preliminary examination of the performance of the new DGT‐P test, compared to existing bicarbonate extractable Olsen and Colwell P tests, for pastures is justified. This study utilized historic data from the Australian National Reactive Phosphate Rock (NRPR) study (1992–1994) that included 25 experimental sites representing a wide range of soil types and climates used for pasture production. Stored (~19 yr) soil samples were analysed for DGT‐P, Olsen P and a single point P buffering index (PBI) and re‐analysed for Colwell P. Results showed the traditional bicarbonate extractable Colwell (r2 = 0.45, P &lt; 0.001) and Olsen P (r2 = 0.27, P &lt; 0.001) methods predicted relative pasture P response more accurately, compared to the novel DGT‐P test (r2 = 0.09, P = 0.03) when all 3 yr of data were examined. We hypothesize that the harsher bicarbonate extraction used for the Olsen and Colwell methods more accurately reflects the ability of perennial pasture roots to access less labile forms of P, in contrast to the DGT‐P test, which does not change the soil pH or dilute the soil and appears unable to fully account for a plants ability to solubilize P. Further studies are needed to compare the capacity of DGT‐P to measure P availability in perennial pasture systems and to better understand the soil chemical differences between pasture and cropping systems.

Can tintinnids be used for discriminating water quality status in marine ecosystems?

Ciliated protozoa have many advantages in bioassessment of water quality. The ability of tintinnids for assessing water quality status was studied during a 7-yearcycle in Jiaozhou Bay of the Yellow Sea, northern China. The samples were collected monthly at four sites with a spatial gradient of environmental pollution. Environmental variables, e.g., temperature, salinity, chlorophyll a (Chl a), dissolved inorganic nitrogen, soluble reactive phosphate (SRP), and soluble active silicate (SRSi), were measured synchronously for comparison with biotic parameters. Results showed that: (1) tintinnid community structures represented significant differences among the four sampling sites; (2) spatial patterns of the tintinnid communities were significantly correlated with environmental variables, especially SRSi and nutrients; and (3) the community structural parameters and the five dominant species were significantly correlated with SRSi and nutrients. We suggested that tintinnids may be used as a potential bioindicator for discriminating water quality status in marine ecosystems.

Phosphorus Fractionation in Soil Cultivated with Sugarcane Fertilized by Filter Cake and Phosphate Sources

Studies of phosphorus (P) forms in high-weathering soils, after long periods of phosphate fertilizer application associated with organic residues, are important to optimize P fertilization. This study aims to evaluate the effect of filter cake application and other distinct phosphate sources on organic and inorganic P fractions in Red Eutrophic Argisoil cultivated with sugarcane. The experiment was established between 2012 and 2014, in Sao Paulo State, Brazil. The treatments were as follows: control (without P), triple superphosphate, natural phosphate from Araxá, and naturally reactive phosphate Bayóvar on the presence and absence of filter cake at 7.5 t ha−1 (dry mass). The P rate was 90 kg ha−1 of phosphorus pentoxide (P2O5) soluble in citric acid. The experiment was arranged in a randomized block, in a 4 × 2 factorial with three repetitions. After 22 months of treatments, soil samples were collected on sugarcane planting lines and P fractionation was analyzed. The greatest percentage of P is found as nonlabile P fractions, regardless of filter cake application or not. The use of low solubility sources, such as natural phosphate from Araxá, in association with filter cake has promoted greater solubility of P bound to calcium (Ca), which can enhance the crop uses. Filter cake increases most of labile and moderately labile inorganic P forms in the soil (resin; sodium bicarbonate, NaHCO3; and sodium hydroxide, NaOH, 0.1 mol L−1), which characterizes the importance of this source to sugarcane nutrient supply.

Water quality upstream and downstream of a commercial oyster aquaculture facility in Chesapeake Bay, USA

Oyster aquaculture is an expanding industry in the Chesapeake Bay. Oysters remove nitrogen (N) and phosphorus (P) from the water column through filtration and conversion of phytoplankton into shell and tissue, but also continuously excrete these same nutrients back into the water column as inorganic compounds readily available for plant or algal uptake. The objective of this study was to assess multiple water quality parameters upstream and downstream of a commercial oyster aquaculture facility in the mesohaline region of the Chesapeake Bay. Results of the study indicated a 78.4% average increase in total ammonia nitrogen (TAN) concentration and a 19.4% decrease in chlorophyll-a (Chl-a) concentration downstream of the facility. There was no significant change in the concentration of reactive phosphate (RP), nitrate–nitrogen (NO3−–N), or nitrite–nitrogen (NO2−–N) as water passed through the facility. It was determined that velocity of water through the facility had no influence on the change in TAN or Chl-a concentration from upstream to downstream of the facility. Increased reduction in Chl-a concentration from upstream to downstream was related to higher upstream concentrations of Chl-a. There was no correlation between increased rates of Chl-a removal and downstream TAN. Results of this study suggest that oyster aquaculture can significantly increase the amount of available inorganic nitrogen in the water column immediately downstream of a facility, independent of upstream availability of phytoplankton and flow velocity of water through the facility.

Spatio-temporal variations in underwater light climate, thermal and chemical characteristics of the tropical soda lake, Lake Shala, Ethiopia

Although soda lakes are highly sensitive to environmental changes and suited for the study of vital ecological processes owing to their unique biological and physicochemical properties and closed nature, there are limited studies on and knowledge of their basic ecology. In this study, temporal and vertical fluctuations of underwater light climate, thermal and chemical characteristics of the soda lake Lake Shala were studied using data collected on 11 occasions over an annual cycle. Measured parameters of underwater light climate depicted light-limited conditions with slight temporal variations, which are attributable to non-biological turbidity and high water column mixing depth. Its water column exhibited superficial thermal stratification with turbulently mixing and well-oxygenated conditions. Alkalinity, pH and conductivity were high but exhibited small temporal and vertical variations. These parameters increased slightly during the rainy season, possibly due to saline inflows associated with precipitation. Most of the major algal nutrients showed small temporal and vertical variations. NO3 − and NH3 in the euphotic zone were often very low or undetectable, while soluble reactive phosphate and total phosphorus were very high throughout the study period. The concentration of SiO2 was remarkably low, which was probably associated with biological uptake and some chemical processes within the lake. In general, physicochemical parameters of Lake Shala exhibited small temporal and vertical variations despite the current threat of environmental degradation, possibly because of the high resilience of the lake associated with its low productivity and voluminous nature.

Preparation, characterization, and bioavailability of a phosphorylated human‐like collagen calcium complex

The aim of this study was to determine whether a phosphorylated human‐like collagen calcium (PHLC–Ca) complex showed a higher bioavailability than other calcium supplements. To improve the calcium‐binding ability of human‐like collagen (HLC), modified HLC was prepared by introducing a reactive phosphate group using a dry‐heating method, followed by the formation of PHLC–Ca in MOPS buffer. PHLC–Ca was characterized using atomic absorption spectrophotometry, Fourier transform infrared (FTIR), fluorescence quenching, circular dichroism (CD), and ultraviolet–visible absorption (UV–vis) spectroscopy. The calcium uptake test showed that the bioavailability of PHLC–Ca was higher than that of CaCl2 and G‐Ca. Data from a mouse model of osteoporosis suggested that PHLC–Ca is superior for treating osteoporosis than CaCl2 or G‐Ca. These results indicate that PHLC–Ca is a desirable calcium supplement for use in daily life and clinical application. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Controls on temporal and spatial variations of phytoplankton pigment distribution in the Northern South China Sea

The seasonal and spatial variations of phytoplankton pigment distribution and their interaction with environmental controlling parameters were investigated in the Northern South China Sea (NSCS) at 37 stations covering the coastal region, the continental shelf, the slope, and the deep-water basin during two summer and two winter cruises from 2010 to 2012. Strong spatial, interseasonal, and intraseasonal variations of pigment distribution were observed in the diverse biogeochemical regions, exhibiting extremely dynamic phytoplankton community structure in the NSCS. In addition to chlorophyll a, the major pigments observed included divinyl chlorophyll a (DV Chl a), total chlorophyll b (Chl b), zeaxanthin (Zea), 19′-hexanoyloxyfucoxanthin (Hex), 19′-but-fucoxanthin (But), fucoxanthin (Fuco), and prasinoxanthin (Pras). Overall, Fuco, Chl b, Zea, Hex, But, and Pras were the dominant pigments in the coastal and shelf region; DV Chl a, Chl b, Hex, But, Zea, and Fuco were the major pigments in the offshore water. After analyzing marker pigment correlations and cellular pigment concentrations, we conclude that Zea, Hex (with But), and Fuco can be used as specific marker pigments for Synechococcus, coccolithophores, and diatoms in the NSCS, respectively. We have also derived that prasinophytes accounted for most of the elevated Chl b observed in the coastal water and appeared to be an important pico-eukaryotic group (Pico) in the coastal region. With varying cellular pigment concentrations observed vertically and seasonally, it is essential to separate sampling stations to different biogeochemical domains to apply pigment to Chl a ratios to estimate phytoplankton community structure in the NSCS. We observed close association between soluble reactive phosphate and Chl a abundance in coastal, shelf, and deep-water regions during summer cruises. Major nutrient supply appears to be the main controlling factor on the temporal and spatial variations of major pigment distribution. The supply is mainly driven by terrestrial input in summer and water mixing strength in winter. During the summer periods, major nutrients are primarily supplied from riverine and groundwater discharge; during winter periods, strong winter monsoon intensifies sub-surface water mixing and results in nutrient and pigment elevation in the euphotic zone. Also driven by the monsoon, the intrusion of the low-temperature coastal current from Taiwan Strait to the coastal region of the NSCS may replace or alter the phytoplankton community in the coastal region in winter. Overall, the temporal and spatial variations of phytoplankton pigment distribution in the NSCS are regulated by the fluctuations of these two major environmental forcings.

Nutrients override atrazine effects on riparian and aquatic plant community structure in a North American agricultural catchment

Summary In agricultural catchments, streams are intimately connected with croplands and are exposed to agrochemicals such as fertilisers and herbicides. In North American streams, the effects of nutrient enrichment on riparian and aquatic plant community structure are not well established and the effects of herbicides are largely unknown. We identified the riparian and aquatic plant community at 12 paired stream/river sites (24 in total, Strahler stream order 3–6) located across a large North American agricultural catchment. Field sites ranged in surrounding agricultural land use (2.7–100% annual crops) and in‐stream June concentrations of reactive phosphate (6–65 μg L−1 as phosphorus) and nitrate (3–3981 μg L−1 as nitrogen). Atrazine, a herbicide commonly used on corn crops in North America, was widespread throughout the catchment with time‐weighted‐average concentrations ranging from 4 to 412 ng L−1 over a 56‐day period. Atrazine concentrations were &gt;100 ng L−1 at over half the field sites. In total, 285 riparian and aquatic plant taxa were identified. Effects of agrochemicals on descriptors of plant communities were assessed by comparing paired sites surrounded by low or high levels of agriculture and examining changes across the catchment. Agrochemicals had no effect on overall species richness. However, the percentage of non‐native species increased across the catchment along a gradient of increasing nitrate. A decline in submerged macrophytes was associated with enrichment of both nitrate and reactive phosphate, whereas no direct effects of atrazine were observed. A floristic quality assessment was used to determine further effects of agrochemicals on riparian and aquatic plant communities. A ranking system, based on native status and tolerance to disturbance, was used to assign coefficient of conservation values to each species. Floristic quality was subsequently calculated as a function of species richness and the average coefficient of conservation value at each site. Overall floristic quality decreased as nitrate increased. Species positively associated with nitrate were typically fast‐growing, weedy, riparian species, whereas species negatively associated with nitrate were characteristic of less disturbed areas and represented a range of growth forms. We conclude that nutrient enrichment, especially of nitrate, has multiple negative effects on riparian and aquatic plant communities that override effects of the herbicide atrazine. Our results highlight the need to reduce inputs of agrochemicals to streams and to regulate nitrogen in addition to phosphorus.

Produção do capim Piatã submetido a diferentes fontes de fósforo

O fósforo é primordial para as plantas forrageiras enquanto a adubação combinada com fontes fosfatadas reativas e naturais podem aumentar a qualidade e a produção do capim Piatã. Objetivou-se avaliar a produção e a relação entre os componentes do capim Piatã submetido a diferentes combinações de fosfato reativo e natural. O experimento foi conduzido em casa de vegetação sob blocos casualizados, com sete repetições. Os tratamentos consistiram de quatro combinações de fontes de fosfato reativo e natural (equivalente a 70 kg ha-1 de P2O5): ausência de adubação fosfatada (controle); adubação com fosfato natural reativo Argélia; adubação com 50% de fosfato natural reativo Argélia e 50% de superfosfato simples e adubação com superfosfato simples. O capim Piatã foi cultivado durante três cortes para caracterização da produção de matéria seca de perfilhos, folhas, pseudocolmo, raízes e relações entre folha/pseudocolmo e parte aérea/raiz. A adubação fosfatada, independentemente da fonte, propiciou incremento na produção da matéria seca das folhas, pseudocolmo e da parte aérea do capim Piatã nos segundo e terceiro cortes avaliativos e na média dos cortes, indicando aumento da produção de forragem.

Spatial differences in the growth rates of Pocillopora damicornis associated with sedimentation rate and light intensity at Polhena patchy reef, southern Sri Lanka

Near shore patchy reef located at the leeward side of the fringing reef at Polhena was surveyed to evaluate spatial patterns of growth rates of Pocillopora damicornis . This study was carried out at three locations of the reef; front, side and back from June to November in 2004. Three sites were selected from each location considering the depth (surface, middle, and bottom). Forty five colonies of P. damicornis which were approximately of the same size were studied. Temperature, dissolved oxygen, BOD5, salinity, pH, soluble reactive phosphorous, turbidity and light intensity of each site were measured fortnightly and their mean values were 28.06 ± 0.24 °C, 8.78 ± 0.15 mg L -1 , 1.40 ± 0.32 mg L -1 , 31.91 ± 3.49 mg L -1 , 8.12 ± 0.04, 8.12 ± 0.01, 20.21 ± 2.05 μg L -1 , 5.78 ± 1.20 NTU, and 49.17 ± 1.97 Lux respectively. Sediments in each site were collected using traps and mean overall sedimentation rate for the experimental period was 45860.6 ± 3364.2 ml m -2 day -1 (2620.6 ± 192.2 g m -2 day -1 ) (n = 36). Growth of coral colonies, which was measured as linear skeletal extension rate (LSER), was 0.15 ± 0.01 mm day -1 . Significant differences in mean light intensity, mean sediment volume, and LSER of coral colonies were observed among different sites. The highest sedimentation rate 94818.2 ± 6981.5 ml m -2 day -1 (5418.2 ± 398.9 g m -2 day -1 ) and the lowest LSER of the colonies (0.05 ± 0.01 mm day -1 ) were observed at back bottom site. The highest LSER was observed at front surface (0.23 ± 0.01 mm day -1 ). LSER showed a significant negative correlation (R 2 = 0.59) with increased sedimentation rate and low light intensity. Back bottom site of the patchy reef was having comparatively unfavorable conditions for the growth of corals that were subjected to more environmental stress than the corals in other sites of the reefs. Sri Lanka J. Aquat. Sci. 20 (1) (2015): 47-58