Without knowing the actual adaptations undertaken, this approach provides limited analysis on economic efficiency. Hanemann argues that Ricardian models may not even capture long-run efficiency because economic agents do not behave optimally even in the long run. Studies of both short-run and mid-to-long run suggest that farmers with access to groundwater will tend to increase pumping, increasing the likelihood of aquifer subsidence, to compensate for losses in surface water or increases in crop water demands . Based on definitions in the latest IPCC report, this is maladaptation more than it is efficient adaptation. Schlenker and Roberts suggest that there is minimal adaptation even in the long run when they find that the results of their isolated time series are similar to those of the isolated cross section. Suffice it to say, that Ricardian approaches are capturing some level of adaptation, but it is likely not economically efficient. Panel data studies on farm profits are not able to capture adaptation even implicitly. In both programming and econometric approaches, vulnerability is measured as loss in economic welfare , which is perhaps the greatest limitation of comparative static approaches. Unlike economic welfare, vulnerability is a dynamic concept. For example,square planter pots the move from field to high-value crops dampens the economic welfare decline caused by a warm-dry climate mid-to-late century. That is, the percentage loss in farm revenue is less than the decline in farm acreage.

However, these high-value crops tend to have lower heat tolerance as temperature increases . Further, field crops are generally regarded as more secure assets with lower associated production costs, than vegetable or tree crops. The concept of vulnerability is able to capture this insecurity. Vulnerability to overall profit loss may be reduced by the crop mix change, but the increased variability in farm income will also increase vulnerability to temperature increases. Medellin-Azuara et al. illustrate this with high-value orchard crops, where the gross revenue declines even as prices increase. Econometric approaches illustrate that California agricultural land value may be particularly vulnerable to changes in surface water supply and nonlinear temperature effects . Deschenes and Kolstad also illustrate that farm profits may be more responsive to climate than annual fluctuations in temperature and precipitation. Several analyses illuminate our understanding of adaptive capacity. The overarching focus for many CALVIN-SWAP studies is to start with a worst-case scenario approach and see how well we fare even with some of the best-case farmer and institutional responses . Joyce et al. also illustrate an example of adaptive capacity through time. Assuming drip irrigation is more widely adopted in the Central Valley by mid-century, they find that groundwater pumping declines. However, as the climate continues to warm towards the end of the century, the positive effects of drip irrigation are eliminated. Beyond this, a discussion of adaptive capacity is lacking. We have moved ahead in the past 15–20 years from the early agro-economic assessments of the early/mid-1990s, but it appears that we are also standing still.

This review has illustrated the various ways comparative static approaches have incorporated adaptive actions to illuminate our understanding of climatic impacts to California agriculture. But, as critics suggest , questions of when and how much farmers and institutions will adapt are left unanswered. Responsiveness — the key characteristic of decision-making — is only vaguely addressed, and, important distributional consequences of climate impacts to agriculture while alluded to, are not identified. Lack of responsiveness and distributional consequences is mostly due to a dearth of individual farm-level data, rather than the incapacity of programming and econometric approaches to accommodate a more specific analysis. Using the same county-level data with more innovations in a comparative static framework could only take programming and econometric approaches so far. There is also a degree of comfort with identifying the primary barrier to moving forward as uncertainty in climate projections. While vulnerability arises out of biophysical processes, it is critical to understand that it is imposed on a pre-existing, dynamic socioeconomic structure . It is important that our economic models do more to capture this structure.Global waterways are impacted by chemical contaminants including pesticides which can negatively impact sensitive species, and human and environmental health. Pesticides with novel modes of action have become increasingly common as they replace older pesticide classes such as organophosphates. The use of both chlorantraniliprole and imidacloprid is widespread and these pesticides of concern are now detected in many surface waters around the world. Chlorantraniliprole detections are frequent in agriculture regions worldwide. Similarly, use of neonicotinoids such as IMI has increased in recent times; IMI is one of the most frequently used insecticides across the world . Imidacloprid and CHL are frequently detected environmental pesticides of concern which affect an organism’s nervous system; however, the extent of their impact on aquatic organisms has not been fully evaluated.

These chemicals have the potential to affect an organism’s behavior due to their impacts on important neurological receptors. Chlorantraniliprole, like other anthranilic diamides, is classified as a Ryanodine Receptor modulator, specifically by activating and competing for binding of the RyR. This receptor affects behavior by altering calcium signaling and muscle movement. Imidacloprid is a neonicotinoid pesticide which interacts agonistically with the postsynaptic nicotinic acetylcholine receptor causing toxic effects to the central nervous system . Despite their relative reduced environmental persistence, these chemicals have been shown to cause adverse effects on non-target aquatic organisms, such as sensitive invertebrate species including the model organism, Daphnia magna. Both of these pesticides have been shown to cause changes in swimming behavior in D. magna. While single-chemical exposure effects are well documented for these novel pesticides of concern, little is known about how CHL and IMI interact in mixtures at environmentally relevant concentrations. An initial seasonal rain event occurring after a period of dry weather, referred to as a “first flush” event, can result in sudden influxes of pesticides into waterways. Runoff or partitioning of water-soluble pesticides into surface waters can affect aquatic health, but certain weather events, like first flush events, can exacerbate this issue. This is especially true in Mediterranean climates, such as California , which are characterized by dry summer months followed by winter rain events. In the absence of irrigation or other mitigating circumstances, this period of little or no rainfall allows pesticide buildup to occur prior to first storm events. First flush events may mobilize pesticides that were applied during extended periods, causing a sudden spike in pesticide concentrations in surrounding waterways. Cladocerans,growing blackberries in containers including Daphnia spp., are the dominant group of zooplankton in many freshwater water bodies, both in biomass and abundance, and can have significant effects on aquatic food chains via their role in the regulation of phytoplankton abundance and competition with other zooplankton. Disruption of this basal trophic level can also result in the reduction of energy transfer efficiency to predators such as fish. Invertebrates which have bio-accumulated pesticides may represent a greater risk to their predators; however, the bio-transformation processes of IMI and CHL are largely unknown for aquatic invertebrates. Survival of model species is a commonly used endpoint for determining the potential toxicity of surface water . This endpoint, however, does not fully capture the adverse effects of chemical exposures, especially when evaluating environmentally relevant concentrations. Behavioral assessments following exposure to sublethal concentrations of pesticides are extremely powerful as they can capture underlying physiological or biochemical conditions, which manifest themselves at the organismal level. This approach can determine ecological risk if the behavior directly relates to factors like survival, growth, or reproduction. Swimming behavioral assays can show adverse effects at much lower chemical concentrations than other commonly measured toxicological endpoints, making them useful for analyzing pesticides at levels far below their lethal concentrations. Swimming behavior is a well-established endpoint in fish studies for pharmacology and toxicology. However, invertebrate species are generally underrepresented. Certain invertebrates have been shown to be more sensitive than most fishes during toxicity testing and are easily obtained and kept in a laboratory setting. Invertebrate behavioral testing has the potential to become a powerful tool in the field of aquatic toxicology and water quality monitoring . Daphnia magna have well defined acutetoxicity testing parameters and are known to demonstrate measurable changes to their natural swimming behavior in response to pesticide exposure, which can be linked with their overall fitness.

Despite these advantages, there are few data evaluating the behavioral effects of complex environmental mixtures on D. magna, an important fish prey and indicator species for multiple sensitive aquatic invertebrates. The Salinas Valley is a highly productive agricultural region which exports a diverse array of agricultural commodities across the world. Due to the intense agricultural activity in this area, complex mixtures of many pesticide classes are frequently detected in runoff. Surface water monitoring has been routinely conducted in this area for more than ten years by the California Department of Pesticide Research and the Central Coast Regional Water Quality Control Board. Analytical chemistry data from these monitoring efforts document frequent detections of many global pesticides of concern, including CHL, IMI, other neonicotinoids, pyrethroids, and other pesticides used in California. Based on this information, we decided to utilize this region as a representative sample of areas with high agricultural use. In this study, we aimed to assess the effects of two emerging pesticides of concern, CHL and IMI, two known neurotoxicants that are frequently found in monitored agricultural waterways at levels exceeding the United States Environmental Protection Agency benchmarks for aquatic life. We evaluated the swimming behaviors of D. magna as sensitive bio-indicators of exposure to a dilution series of surface water samples collected from an agricultural region , during an extended dry period, and after a first flush event. We used a dilution series with surface water concentrations ranging from 100% to 6% in order to observe a wide range of toxicological outcomes. To isolate the effects of these two pesticides from other chemicals present in these mixtures, we also evaluated the survival and swimming behaviors of D. magna after acute exposures to single and binary mixtures of CHL and IMI, at concentrations relevant to those observed in surface water. We performed all exposures following US EPA protocols. For field exposures, we placed twenty individuals into each of the 250 mL replicate beakers containing 200 mL of treatment water, with four replicates per treatment. We used larger exposure volumes for the field water to reduce the potential influence of sediment on organism toxicity, and to follow EPA guidelines for acute exposures to effluent. For CHL and IMI exposures, we exposed six organisms in 20 mL scintillation vials, with six replicates per treatment, per time point. We randomly chose 24 individuals per treatment group to use in behavioral assays. We conducted all exposures in temperature-controlled chambers kept at 20 ± 2 ◦C, with a 16 h:8 h light:dark cycle to maintain optimal conditions for our test organisms. Every day during the exposure, we recorded the number of organisms per beaker and the mortality, while removing dead individuals from the tests. At the 48 h mark, we performed water changes; 80% volume was exchanged in surface water exposures to account for suspended solids and additional bacterial activity seen in field samples, and 50% water changes for CHL/IMI exposures. We tested temperature, total alkalinity, hardness, pH, and dissolved oxygen in situ using a YSI EXO1 multi-parameter water quality sonde at both test initiation and 48 h to ensure that the water remained within the acceptable ranges for D. magna. We fed all organisms at both the test initiation and after 48 h water renewals. We targeted sampling sites located in the Salinas River and surrounding waterways which correspond to long-term monitoring sites. Data from these sites include more than 10 years of historical chemical analysis data. Historically, some pesticide detections exceeded EPA Benchmarks for Aquatic Life. These sites are also located near ecologically sensitive areas and are thus of interest for monitoring water quality. These sampling sites are also located downstream of highly productive agricultural regions and residential areas, leaving them at high risk for contamination of complex mixtures. We sampled surface water before and ~24 h after a first flush event from these sites. We collected samples from well mixed, wadable waters using 1 L amber glass bottles certified to meet current EPA guidelines, sealed with Teflon-lined lids. Immediately after collection, we placed samples in coolers on wet ice for transportation, then refrigerated them at 4 ◦C upon arrival in the lab.