Evaluating the contribution of subsurface drainage to watershed water yield using SWAT+ with groundwater modeling.

Drainage outflow from artificial subsurface drains can be a significant contributor to watershed water yield in many humid regions of the world. Although many studies have undertaken to simulate hydrologic processes in drained watersheds, there is a need for a study that first, uses physically based spatially distributed modeling for both surface and subsurface processes; and second, quantifies the effect of surface and subsurface parameters on watershed drainage outflow. This study presents a modified version of the SWAT+ watershed model to address these objectives. The SWAT+ model includes the gwflow module, a new spatially distributed groundwater routine for calculating groundwater storage, groundwater head, and groundwater fluxes throughout the watershed using a grid cell approach, modified in this study to simulate the removal of groundwater by subsurface drains. The modeling approach is applied to the South Fork Watershed (583 km2), located in Iowa, USA, where most fields are drained artificially. The model is tested against measured streamflow, groundwater head at monitoring wells, and drainage outflow from a monitored subbasin. Sensitivity analysis is then applied to determine the land surface, subsurface, and drainage parameters that control subsurface drainage. Simulated drainage flow fractions (fraction of streamflow that originates from subsurface drainage) range from 0.37 to 0.54 during 2001-2012, with lower fractions occurring during years of high rainfall due to the increased volumes of surface runoff. Subsurface drainage comprises the vast majority of baseflow. Results indicate surface runoff and soil percolation parameters have the strongest effect on watershed-wide subsurface drainage rather than aquifer and drain properties, pointing to a holistic watershed approach to manage subsurface drainage. The modeling code presented herein can be used to simulate significant hydrologic fluxes in artificially drained watersheds worldwide.

Using nutrient transport data to characterize and identify the presence of surface inlets in regions with subsurface drainage.

Surface inlets route ponded surface water into subsurface drainage networks and are prevalent throughout North America. Despite serving as a nutrient loss pathway, contributing to downstream water quality degradation, surface inlets are thought to be underreported in drainage studies within the literature. Previous studies have demonstrated the footprint that surface inlets have on nutrient transport and drainage effluent but are site specific and focused on individual events. Moreover, although their ubiquitous presence is assumed, no regional surface inlet database exists. To this end, a structured review was undertaken with two goals. First, the MANAGE Drain Load database, consisting of nearly 1,500 site-years of drainage and nutrient data, was analyzed to determine distinctions between areas with and without surface inlets. The median annual total phosphorus (TP) load was greater at site-years with surface inlets (0.40 kg ha-1 ) than site-years without (0.21 kg ha-1 ). The opposite emerged for dissolved nitrogen (DN) loads as site-years with surface inlet had a smaller median annual load (3.3 kg ha-1 ) than site-years without (23.0 kg ha-1 ). This relationship is attributed to immobile TP being transported primarily through overland flow and routed to subsurface drains via surface inlets and to relatively more mobile DN being subsurface driven, bypassed in settings with surface inlets. No statistical differences were found in annual drainage or ratios of particulate P to TP between site-years with and without surface inlets. Second, a logistic regression model was developed that predicts the presence of surface inlets within MANAGE. Eighteen percent of site-years and 21% of sites were predicted to have surface inlets.

Caudate nucleus in retrieval of trace eyeblink conditioning after consolidation.

Trace eyeblink conditioning (EBC) is an associative learning task in which a stimulus-free trace period separates the presentation of a behaviorally neutral conditioned stimulus (CS; whisker stimulation) from a behaviorally salient unconditioned stimulus (US; air puff to the eye). Repeated pairings of the CS with the US results in the emergence of the conditioned response (CR; eyeblink after CS presentation and before US presentation). The goal of these experiments was to determine whether the caudate nucleus (CN) plays a role in retrieval of previously acquired trace EBC after memory consolidation. Lesions of the CN were made 1 month after initial trace EBC. CN-lesioned rabbits performed fewer adaptive CRs and more short-latency non-adaptive responses than sham-lesioned controls. They were not able to improve their CR performance after consolidation as were controls. Single-unit recordings taken from separate cohorts of rabbits demonstrated that neurons in the CN were still responsive to the CS and US 1 month after initial trace EBC, particularly in the medial and ventral CN on trials when a CR occurred. The proportion of rate-increasing neurons was higher in trace-conditioned than in pseudo-conditioned rabbits. Neurons in regions destroyed in the behavioral experiment demonstrated prolonged firing during the trace period, which might underlie the results from the behavioral experiment. These data demonstrate that the CN plays an important role in retrieval of a previously learned associative task after memory consolidation has occurred.

Infragranular barrel cortex activity is enhanced with learning.

The barrel cortex (BC) is essential for the acquisition of whisker-signaled trace eyeblink conditioning and shows learning-related expansion of the trained barrels after the acquisition of a whisker-signaled task. Most previous research examining the role of the BC in learning has focused on anatomic changes in the layer IV representation of the cortical barrels. We studied single-unit extracellular recordings from individual neurons in layers V and VI of the BC as rabbits acquired the whisker-signaled trace eyeblink conditioning task. Neurons in layers V and VI in both conditioned and pseudoconditioned animals robustly responded to whisker stimulation, but neurons in conditioned animals showed a significant enhancement in responsiveness in concert with learning. Learning-related changes in firing rate occurred as early as the day of learning criterion within the infragranular layers of the primary sensory cortex.

Local pretreatment with the cannabinoid CB1 receptor antagonist AM251 attenuates methamphetamine intra-accumbens self-administration.

The endocannabinoid system is a potential target for therapeutic intervention of substance abuse. Cannabinoid CB1 receptor antagonist decreases intravenous methamphetamine self-administration in animal models. This study examined whether the nucleus accumbens (NAcc) is a site of interaction between methamphetamine and the CB1 receptor antagonist AM251. Male Sprague-Dawley rats were trained to lever press and then were surgically implanted with a guide cannula into the right NAcc. Rats were allowed one week to recover and then AM251 (0.1 or 1.0 µg/µL) was reverse dialyzed directly into the NAcc prior to methamphetamine (10 µg/µL) intra-accumbens self-administration. AM251 (1.0 µg/µL) reduced methamphetamine self-administration while AM251 (0.1 µg/µL) had an intermediary effect. The mechanism of self-administration attenuation is not known but could be mediated by AM251 affecting the negative feedback from the NAcc to the ventral tegmental area (VTA). This study provides evidence that the endocannabinoid system is involved with rewarding effects of methamphetamine and suggests a possible therapeutic intervention for methamphetamine abuse.

Caudate nucleus is critically involved in trace eyeblink conditioning.

The basal ganglia are a collection of brain regions involved with motor planning and initiation. The major site of cortical and thalamic input into the basal ganglia network is the striatum, which includes a differentiated caudate nucleus (CN) and the putamen in rabbits. Trace eyeblink conditioning (EBC) is a forebrain-dependent associative learning task in which a stimulus-free time interval separates the presentation of a behaviorally neutral conditioned stimulus (CS) and a behaviorally salient unconditioned stimulus. We investigated whether the CN is essential for acquisition of trace EBC and whether learning-related changes in neuronal activity occur in the caudate nucleus during trace EBC. Bilateral lesions of the CN in rabbits prevent acquisition of trace EBC. In separate cohorts of rabbits, single-unit recordings showed that medium spiny neurons from regions shown to be critical by lesions display strong responses to the CS, especially in the initial days of training before acquisition. Cholinergic interneurons, or tonically active neurons, become responsive to the CS and show dramatic firing rate changes during the trace interval after learning criterion has been met. These data demonstrate that the CN is required for and involved in trace EBC.