For maximum benefit, vegetative buffers should be sized for the treatment area based on the expected runoff volumes for a particular operation . In short, Liu et al. reviewed 80 experiments, and meta-analyses of these data indicated that sediment removal was maximized with a 10-m buffer width and 9% slope, regardless of the ratio of buffer area to watershed area. A review of 11 studies by Dorioz et al. evaluated vegetated buffer strip efficacy for a range of contaminants which reported that remediation efficacy ranges from 47 to 100% for nitrogen, −64 to +93% for total phosphorus, and −83 to +89% for dissolved phosphorus. Phosphorus mitigation is of particular concern, since it is difficult to remove from soil and aquatic systems. Sediment removal ranged from 40 to 100%, depending upon vegetation type and growth stage, slope, and buffer width . Otto et al. reported pesticide removal efficacies ranging from 81 to 99% for metolachlor and 74 to 99% for terbuthylazine .Carbon Media Three types of carbon-based denitrification bioreactors are commonly used to mitigate nitrate-rich subsurface runoff: beds, layers, and walls. Denitrification beds, also known as wood-chip bioreactors, are containers filled with a carbon-rich material; this type shows the most promise for management of irrigation runoff from specialty crop production areas. Denitrification layers consist of horizontal layers of carbon-rich material, cultivo del arandano while denitrification walls consist of carbon-based material installed vertically in the ground through which groundwater flows are intercepted . These systems have been applied extensively in agricultural production regions throughout the world. Bioreactors are installed using a carbon-based substrate such as bark, wood chips, mulch, sawdust, straw, or carbon from various other waste products .

Carbon-rich substrates serve as both electron donors and sources of cellular material for microbial communities in the bioreactors . More information is needed with regard to carbon source quality and longevity of denitrification support, as high-quality carbon sources can support denitrification for 9–15 years . In these bioreactors, nitrogen-rich runoff water flows through a carbon based substrate, and anaerobic conditions within the media promote reduction of nitrate-N to N2 gas. Bioreactor cells are filled with an artificial media, typically a plastic substrate with uniform particle sizes and shapes. Artificial media provide a surface area that is colonized by microbial populations that facilitate contaminant remediation, but a supplemental carbon source is required to support growth and energetic needs of microbial communities. These systems have been used to manage nitrogen in a range of industrial applications . Wilson and Albano used a Kaldnes media with a molasses-based carbon source to reduce nitrogen-rich irrigation runoff at a Florida nursery from 5.9–11.9 mg L−1 to 0.1–1.0 mg L−1 , an 86 to 97% reduction, when adequate carbon was supplied to the system. Unintended negative consequences of the use of denitrification bioreactors are also possible: nitrate transformation may be incomplete, potentially releasing nitrous oxide , a potent greenhouse gas ; the release of carbon dioxide or methane may occur during degradation of organic matter ; or methylation of mercury can occur if all nitrate is reduced and sulfate-reducing bacteria are active .Algal turf scrubbers use sheet flow and a large surface area to grow algae for nutrient removal .Every few days, dependent on temperature, algae are scraped off the surface, and the biomass is collected while remaining algae continue to grow.

The algae uptake N and P from the water, and harvesting the algae removes N and P from the system. The harvested algae can then be used as a fertilizer, a biofuel feedstock, or otherwise as a nutrient source or soil/substrate amendment. Turf scrubbers can be easily sized from operational to watershed scale if enough land is available, with the ability to treat 40–80 million liters per day or more. Algal turf scrubbers have been found to produce 5 to 10 times the biomass of land-based systems, potentially decreasing the amount of land required for remediation . In dairy operations, Pizarro et al. reported that ATS costs averaged $450 to $650 per cow per year, while dairy cows averaged $500 annual profit per animal. This assessment did not take into account any products that were sold from the algae produced, nor the environmental benefit of removing those nutrients from the environment. Mulbry et al. noted that even at $780 per cow per year for operating an ATS, that amounted to $11 for removing 1 kg of N, much less expensive than many other options such as wastewater treatment plant upgrades. At loading rates of 0.3 to 2.5 g total N and 0.08 g to 0.42 g total P per square meter per day, algae were able to produce a biomass of 2.5 to 25 g dry weight per square meter per day, of which 7 and 1% were N and P on average, respectively . Small-scale ATS were also shown to be effective when installed directly into waterways in the Chesapeake Bay watershed, remediating on average 250 mg total N and 45 mg total P per square meter per day at the most productive site, which equates to 380 kg N per ha and 70 kg P per ha, based on 150 days of operation per year . Craggs et al. found a higher rate of P removal at 730 mg per square meter per day in a similar system, which was based on an average of 2.1% P by dry weight. Optimization of ATS systems depend on a number of factors including flow rate, pulsed vs. constant flow, pH, and whether systems are run continuously or only running during the day .

Additional research to address these issues for growers would be beneficial. The feasibility of ATS for nursery production will be largely dependent on the amount of land available, installation and maintenance costs, and the benefit that the operation realizes in regards to nutrient runoff reduction.Although each of the treatment technologies discussed above can help reduce environmental impacts associated with production runoff, additional gains in treatment efficacy can be realized via pairing two or more types of treatment systems in series or other combinations which are synonymous with treatment train or chain. This coupling is often most effective when targeting different types of physical, chemical, and biological contaminants , since there is no single treatment system that will effectively manage all types of contaminants . Much of the research with treatment trains has been focused on storm water runoff and wastewater treatment systems , with fewer studies focused on agricultural water treatment trains for container-grown crop production. Kabashima et al. demonstrated treatment train efficacy at treating nursery production runoff via use of PAM injection paired with sediment traps and 340 m of vegetated buffers that increased sediment, bifenthrin, cis-permethrin, and transpermethrin removal by 5.6% , 12.1% , 9.8% , and 20.5% , respectively. We do not know if there is a practical limit to the number of treatment options that can be applied in series, or if the order in which they are placed influences the relative efficacy of treatment for specific contaminants. These considerations need to be addressed so that science-based recommendations for treatment-train use at commercial growing facilities are available. As environmental regulations become stricter or additional economic benefits are realized in the future,maceta hidroponica specialty crop producers will likely install water treatment technologies either singly or in treatment trains. The costs and efficacies of these treatment systems need further validation to encourage adoption of treatment technologies. On-site evaluations of treatment system efficacy will confirm scalability and transferability of treatment efficacy across production systems. Hong and Moorman and Raudales et al. noted that little efficacy information is available for container production settings other than chlorination. Some technologies have been trialed at nursery and greenhouse operations [e.g., constructed wetlands ; carbon filters ; PAM and sediment traps ; bioreactors ], but in other instances cited research has been conducted in alternate agricultural production systems or for industrial wastewater treatment .The ability to grow plants in soilless substrates and plastic containers has produced a major shift from in ground to above ground production of specialty crops. Above ground plant production has necessitated the application of large volumes of irrigation water compared with field production, which can lead to sediment loss and chemical runoff. Application of agrichemicals to modify plant growth and control pest and plant disease problems can impact the water quality of both surface water and groundwater, either on-site or in the surrounding environment if the proper precautions are not taken to protect waterways. A number of BMPs exist to mitigate sediment and chemical runoff from agricultural production, including water recapture and reuse. Significant grower concerns exist regarding the chemical and biological contaminants that may be reapplied to plants if operational water is reused. In order to mitigate these concerns and explain the current state of information related to water remediation, we discuss a number of management practices for the remediation and reuse of water at an operation or release into the environment after treatment.

Various forms of water filtration remove organic material resulting in increased disinfection efficacy . Compounds can be used to bind chemicals of concern. Sediment and any compounds bound to it can be removed in a number of ways including sediment traps and filter socks. Biological treatment options can remove physical, chemical, and biological contaminants. Treatment BMPs can be used in series or parallel, depending on operational requirements and the contaminant to be removed from the water. Each BMP differs in installation and maintenance costs and has both benefits and drawbacks that need to be considered prior to implementation. In some areas, additional research is required to provide growers and consultants with rigorous science-based information related to the efficacy and longevity of treatment options. There is the potential for more stringent regulations to be enacted internationally and in the USA at the federal, state, and local level to address water quality problems . A number of areas in the USA and throughout the world have approved regulations restricting agricultural water use or runoff. Restrictions are likely to increase over time with increasing population numbers and changing climate patterns, which will strain surface water and groundwater resources. Future regulations, in terms of how much an agrichemical load or concentration must be reduced, and incentives available for implementing various practices will likely impact adoption rates of various contaminant-specific, scientifically vetted remediation BMPs. These regulations may target container grown specialty crop production specifically or agriculture in general. It is important to have both cost and efficacy information available, so that producers can make informed decisions. Proactive growers may voluntarily choose to remediate potential problems at their operation by replacing or repairing broken, leaking, or inefficient systems, which would reduce water use and subsequent runoff and use appropriate BMPs where possible, including water storage, treatment, and reuse facilities at their operation. It is recommended that growers document changes, including cost, to show good faith efforts to improve their operation’s environmental sustainability. Growers can be disincentivized to make changes at their operation, since these investments may not be counted in their favor if new regulations are passed. If for example, regulations are implemented requiring irrigation volumes to be reduced, they could allow waivers for growers who have documented past irrigation reductions due to better management practices. A major goal of research is to provide information for individuals and society to make the best decisions for people and the environment. Science-based recommendations are an important foundation for mitigating water challenges of the present and the future. As regulations change, specialty crop producers will need to remain flexible, and research is needed to continue to provide viable solutions to the issues that are faced by growers, as well as to ameliorate potential environmental problems in surface water and ground water.Investigations of the dynamics of economic inequality across distinct economic systems have been limited by the paucity of data on all but contemporary market-based industrial societies. They are also hampered by the lack of an empirically based model applicable to the differing institutions and technologies characteristic of the broad range of economic systems, ranging from hunter-gatherers through pastoral and agrarian societies to modern economies. Here we present empirical estimates of the extent of inheritance of wealth across generations and of the degree of wealth inequality, along with a descriptive model of the relation between the two. We support our model with data on three distinct wealth classes— material, embodied, and relational, to be defined below—in 21 contemporary and recent hunter gatherer, horticultural, pastoral, and agricultural populations.