Hortonian Scaling of Coupled Hydrological and Biogeochemical Responses Across an Intensively Managed River Basin

Structural and functional attributes across fractal river networks have been characterized by well-established and consistent hierarchical, Hortonian scaling patterns. In most of the global river basins, spatial patterns of human settlements also conform to similar hierarchical scaling. However, emergent spatial hierarchical patterns and scaling of heterogeneous anthropogenic nutrient loads over a river basin are less known. As a case study, we examined here a large intensely managed river basin in Germany (Weser River; 46K km(2); 8M population). Archived data for point-/diffuse-sources of total Phosphorus (P-tot) input loads were combined with numerical and analytical model simulations of coupled hydrological and biogeochemical processes for in-stream P-tot removal at the network scale. We find that P-tot input loads scale exponentially over stream-orders, with the larger scaling constant for point-source loads from urban agglomerations compared to those for diffuse-source contributions from agricultural and forested areas. These differences in scaling patterns result from hierarchical self-organization of human settlements, and the associated clustering of large-scale, altered land-cover. Fraction of P-tot loads removed through in-stream biogeochemical processes also manifests Hortonian scaling, consistent with predictions of an analytical model. Our analyses show that while smaller streams are more efficient in P-tot removal, in larger streams the magnitude of P-tot loads removed is higher. These trends are consistent with inverse scaling of nutrient removal rate constant with mean discharge, and downstream clustering of larger cumulative input loads. Analyses of six nested sub-basins within the Weser River Basin also reveal similar scaling patterns. Our findings are useful for projecting likely water-quality spatial patterns in similar river basins in Germany, and Central Europe. Extensions and generalizations require further examination of diverse basins with archetype spatial heterogeneities in anthropogenic pressures and hydroclimatic settings

Remediation of Contaminated Soils by Solvent Flushing

Solvent flushing is a potential technique for remediating a waste disposal/spill site contaminated with organic chemicals. This technique involves the injection of a solvent mixture (e.g., water plus alcohols) that enhances contaminant solubility, reduces the retardation factor, and increases the release rates of the contaminants. A simulation model is developed to predict contaminant elution curves during solvent flushing for the case of one‐dimensional, steady flow through a contaminated medium. Column experiments are conducted with a Eustis fine sand that is initially equilibrated with an aqueous naphthalene solution, and then eluted with different methanol‐water mixtures to remove the naphthalene. The model simulations, based on parameter values estimated from literature data, agree well with the measured elution profiles. Solvent flushing experiments, where the soil was initially equilibrated with a solution of naphthalene and anthracene, show that compounds with different retardation factors are separated at low cosolvent contents, while coelution of the compounds occurs at higher contents. In general, the smaller the retardation factor in water and the higher the cosolvent fraction, the faster the contaminant is recovered. The presence of nonequilibrium conditions, soil heterogeneity, and type of cosolvent will influence the time required to recover the contaminant.\u

Evaluation of claw development in giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879)

Dynamics of claw development in Macrobrachium rosenbergii (de Man, 1879) was evaluated through monosex culture. The segregated males and females were stocked separately in two earthen ponds of 200 m2 area, at a density of 2.5 m-2 and reared for 3 months. Percentage contribution of claw weight to body weight (PCB) increased from 8.96 to 14.4% in the first month, but the change was minimal (14.4 to 17.19%) during the rest of the culture period. In order to delineate the relationship further, the data obtained was pooled together and classified into different classes based on the body weight (class interval 10 g). Interestingly, PCB in males decreased gradually upto 30 - 40 g weight class and then increased considerably for higher weight classes. But for females, the increase in PCB was marginal

Emergent spatial patterns of competing benthic and pelagic algae in a river network: A parsimonious basin-scale modeling analysis.

Algae, as primary producers in riverine ecosystems, are found in two distinct habitats: benthic and pelagic algae typically prevalent in shallow/small and deep/large streams, respectively. Over an entire river continuum, spatiotemporal patterns of the two algal communities reflect specificity in habitat preference determined by geomorphic structure, hydroclimatic controls, and spatiotemporal heterogeneity in nutrient loads from point- and diffuse-sources. By representing these complex interactions between geomorphic, hydrologic, geochemical, and ecological processes, we present here a new river-network-scale dynamic model (CnANDY) for pelagic (A) and benthic (B) algae competing for energy and one limiting nutrient (phosphorus, P). We used the urbanized Weser River Basin in Germany (7th-order; ~8.4 million population; ~46 K km2) as a case study and analyzed simulations for equilibrium mass and concentrations under steady median river discharge. We also examined P, A, and B spatial patterns in four sub-basins. We found an emerging pattern characterized by scaling of P and A concentrations over stream-order ω, whereas B concentration was described by three distinct phases. Furthermore, an abrupt algal regime shift occurred in intermediate streams from B dominance in ω≤3 to exclusive A presence in ω≥6. Modeled and long-term basin-scale monitored dissolved P concentrations matched well for ω>4, and with overlapping ranges in ω<3. Power-spectral analyses for the equilibrium P, A, and B mass distributions along hydrological flow paths showed stronger clustering compared to geomorphological attributes, and longer spatial autocorrelation distance for A compared to B. We discuss the implications of our findings for advancing hydro-ecological concepts, guiding monitoring, informing management of water quality, restoring aquatic habitat, and extending CnANDY model to other river basins

Real-time forecasting of pesticide concentrations in soil

peer-reviewedForecasting pesticide residues in soils in real time is essential for agronomic purposes, to manage phytotoxic effects, and in catchments to manage surface and ground water quality. This has not been possible in the past due to both modelling and measurement constraints. Here, the analytical transient probability distribution (pdf) of pesticide concentrations is derived. The pdf results from the random ways in which rain events occur after pesticide application. First-order degradation kinetics and linear equilibrium sorption are assumed. The analytical pdfs allow understanding of the relative contributions that climate (mean storm depth and mean rainfall event frequency) and chemical (sorption and degradation) properties have on the variability of soil concentrations into the future. We demonstrated the two uncertain reaction parameters can be constrained using Bayesian methods. An approach to a Bayesian informed forecast is then presented. With the use of new rapid tests capable of providing quantitative measurements of soil concentrations in the field, real-time forecasting of future pesticide concentrations now looks possible for the first time. Such an approach offers new means to manage crops, soils and water quality, and may be extended to other classes of pesticides for ecological risk assessment purposes

Globally Universal Fractal Pattern of Human Settlements in River Networks

River networks play a key role in the spatial organization of human settlements. Both river networks and human settlements have been found to exhibit regular self-similar patterns, but little is known about the generalized spatial patterns of human settlements embedded within river networks. Here based on night light data, we find a universal fractal structure at the global scale, with both robust Hortonian scaling relationships with the extent of human settlements and statistically significant power law scaling of the power spectra of human area functions. Globally, we find consistent patterns of power law preferential downstream clustering of human settlements across all six populated continents, typically up to 40% of the maximum flow length. This downstream clustering suggests an optimum distribution of humans in large river basins for trade, transport, and natural resource utilization but with attendant implications for human impacts on rivers. Recognition of such spatial patterns helps generalize assessments of human impacts on rivers, with direct implications for management of water quality and biological diversity in river networks

Design, development and construction of open sea floating cage device for breeding and farming marine fish in Indian waters

The floating cage device described in the present study is the first of its kind in Indian seas and consists of a cylindrical floating cage structure along with suitable netting materials for mariculture of finfishes and shellfishes in open sea. The cage structure was made of high density polyethylene (HDPE) top support, inner and outer rings and a middle catwalk. The inner and outer collar had provisions for connecting outer predator, inner growout and bird nets. Catwalk in the middle served for regular cage management and safety of the workers. There were HDPE vertical and diagonal supports for the cage frame. Ballast was used at the bottom to maintain the shape of the cage. The total weight of the cage frame was 447.7 kg in air and 74.2 kg in water. The floatation force of the cage was 211.2 kg while the effective floatation force was 131.8 kg. The total weight of netting materials including rope was 46.7 kg in air and 5.2 kg in water. A floating net cage device of 6 m inner and 8 m outer collar dia with 6 m net depth and an effective inner volume of 169.7 m3 was designed and successfully tested in open sea, during the present study. The floating sea cage structure and nets were designed and standardised in such a way to suit the current and wave conditions of Indian seas