Michael R. Burchell

INFLUENCE OF PATCH SIZE AND SHAPE ON OCCUPANCY BY SHRUBLAND BIRDS

Abstract. Populations of many shrubland bird species are declining in the eastern United States. Efforts to restore shrubland and early-successional forest may help to ameliorate these declines. However, uncertainty remains about how the size and shape of habitat patches and the surrounding habitat matrix affect patch occupancy by shrubland passerines. Our objectives were to determine if shrubland birds avoid small or irregularly shaped habitat patches and to identify minimum area requirements for area-sensitive species. Additionally, we sought to determine if the proportion of mature forest cover in the landscape influences patch occupancy. We surveyed 35 individual habitat patches in 2007 and 43 in 2008 for the presence of eight shrubland birds. Then, we modeled the probability of five of these species occupying an individual patch relative to patch area, patch shape, and percent forest cover within 1 km of the patch. We documented evidence of area sensitivity for the Yellow-breasted Chat (Icteria virens) and Prairie Warbler (Setophaga discolor) and estimated their minimum area requirements at 2.3 and 1.1 ha, respectively. The Blue Grosbeak (Passerina caerulea) also was area-sensitive in irregularly shaped patches. Predicted patch-occupancy probability was >0.9 in patches ≥5.5 ha for all area-sensitive species. Patch shape alone and proportion of forest cover were not important predictors of occupancy for these shrubland birds. Restored shrubland and early-successional forest in agricultural landscapes can provide habitat for many shrubland birds, but patches should be >5 ha to maximize shrubland bird diversity.

Cropland Edge, Forest Succession, and Landscape Affect Shrubland Bird Nest Predation

ABSTRACT The effects of habitat edges on nest survival of shrubland birds, many of which have experienced significant declines in the eastern United States, have not been thoroughly studied. In 2007 and 2008, we collected data on nests of 5 shrubland passerine species in 12 early successional forest patches in North Carolina, USA. We used model selection methods to assess the effect of distance to cropland and mature forest edge on nest predation rates and additionally accounted for temporal trends, nest stage, vegetation structure, and landscape context. For nests of all species combined, nest predation decreased with increasing distance to cropland edge, by nearly 50% at 250 m from the cropland edge. Nest predation of all species combined also was higher in patches with taller saplings and less understory vegetation, especially in the second year of our study when trees were 4–6 m tall. Predation of field sparrow (Spizella pusilla) nests was lower in landscapes with higher agricultural landcover. Nest predation risk for shrubland birds appears to be greater near agricultural edges than mature forest edges, and natural forest succession may drive patterns of local extirpation of shrubland birds in early successional forest patches. Thus, we suggest that habitat patches managed for shrubland bird populations should be considerably large or wide (>250 m) when adjacent to crop fields and maintained in structurally diverse early seral stages.

Relationships Between Nitrogen Transformation Rates and Gene Abundance in a Riparian Buffer Soil

Denitrification is a critical biogeochemical process that results in the conversion of nitrate to volatile products, and thus is a major route of nitrogen loss from terrestrial environments. Riparian buffers are an important management tool that is widely utilized to protect water from non-point source pollution. However, riparian buffers vary in their nitrate removal effectiveness, and thus there is a need for mechanistic studies to explore nitrate dynamics in buffer soils. The objectives of this study were to examine the influence of specific types of soluble organic matter on nitrate loss and nitrous oxide production rates, and to elucidate the relationships between these rates and the abundances of functional genes in a riparian buffer soil. Continuous-flow soil column experiments were performed to investigate the effect of three types of soluble organic matter (citric acid, alginic acid, and Suwannee River dissolved organic carbon) on rates of nitrate loss and nitrous oxide production. We found that nitrate loss rates increased as citric acid concentrations increased; however, rates of nitrate loss were weakly affected or not affected by the addition of the other types of organic matter. In all experiments, rates of nitrous oxide production mirrored nitrate loss rates. In addition, quantitative polymerase chain reaction (qPCR) was utilized to quantify the number of genes known to encode enzymes that catalyze nitrite reduction (i.e., nirS and nirK) in soil that was collected at the conclusion of column experiments. Nitrate loss and nitrous oxide production rates trended with copy numbers of both nir and 16s rDNA genes. The results suggest that low-molecular mass organic species are more effective at promoting nitrogen transformations than large biopolymers or humic substances, and also help to link genetic potential to chemical reactivity.

Impact of storm-water runoff on clogging and fecal bacteria reduction in sand columns.

Storm-water runoff has been identified as a major cause of coastal water quality degradation. Storm-water outfalls, common in many coastal towns, convey bacteria and other pollutants into the ocean and estuaries. In an effort to minimize this impact, the Town of Kure Beach, North Carolina, installed Dune Infiltration Systems (DIS) at two storm-water outfalls to receive storm-water runoff and allow infiltration beneath the beach dunes. A laboratory column experiment was performed to supplement this installation and determine the potential hydraulic and bacterial removal efficiency of the sand comprising the Kure Beach dunes. Columns constructed using sand collected at different depths of the dune were used to analyze the affect of bacteria application on infiltration and to examine the changes in bacteria removal that occur as infiltration rates are affected by bacteria-laden water application. Sand columns were loaded over a 60-day period with either bacteria-free storm water or storm water spiked with Es...

SHALLOW SUBSURFACE DRAINS TO REDUCE NITRATE LOSSES FROM DRAINED AGRICULTURAL LANDS

Nitrate losses from subsurface drainage systems remain an important environmental concern. Data were collected from two drainage systems near Plymouth, North Carolina, to evaluate the effect of subsurface drain depth on nitrate-nitrogen (NO3 --N) losses. Drains in plot 1 were 1.5 m deep and 25 m apart, and drains in plot 2 were 0.75 m deep and 12.5 m apart. Both plots received swine wastewater applications. Overall, the shallow drainage system had 42% less outflow than the deeper drainage system. Lower NO3 --N concentrations were observed in the shallow groundwater beneath the shallow drainage plots as a result of higher water tables and likely increased denitrification. However, NO3 --N concentrations in the drainage water from the shallow drains were not reduced. On average, NO3 --N export from the shallow subsurface drains was 8 kg ha-1 in 2001 and 27 kg ha-1 in 2002. Nitrate export from the deeper drains was 6 kg ha-1 in 2001 and 37 kg ha-1 in 2002. Decreased export observed in 2002 from the shallow subsurface drainage system was significant at the 10% level, but not for the entire 21-month period. Longer-term field studies, which incorporate variable climatological events, are needed to conclude whether shallower drain depth will reduce NO3 --N export from subsurface drainage systems.

Addressing the Fouling of In Situ Ultraviolet-Visual Spectrometers Used to Continuously Monitor Water Quality in Brackish Tidal Marsh Waters

The introduction of portable in situ ultraviolet-visual spectrometers has made possible the collection of water quality parameters at a high frequency in dynamic systems such as tidal marshes. The usefulness of this technology is inhibited by fouling of the instruments optics. In this study, a spectrometer fitted with manufacturer-recommended compressed air optical cleaning was installed in a brackish marsh to determine if fouling interfered with measurements between bi-weekly servicing. During a 2-wk period, the absorbance measured in air at 220 nm increased from 9 to 549 m, indicating major fouling. An antifouling system was developed that reduced the time of exposure of the optics to stream water and used a pressurized fresh water cleaning. After implementation of the system, the absorbance in air increased to at most 63 m after 2 wk of data collection. The dramatic reduction in fouling will allow quality long-term data to be collected using this technology.

Effects of Riparian Buffer Vegetation and Width: A 12-Year Longitudinal Study.

Agricultural contributions of nitrogen are a serious concern for many water resources and have spurred the implementation of riparian buffer zones to reduce groundwater nitrate (NO). The optimum design for buffers is subject to debate, and there are few long-term studies. The objective of this project was to determine the effectiveness over time (12 yr) of buffer types (trees, switchgrass, fescue, native, and a control) and buffer widths (8 and 15 m) by measuring groundwater NO-N and dissolved organic carbon (DOC) trends. At the intermediate groundwater depth (1.5-2.1 m), NO-N reduction effectiveness was 2.5 times greater (46 vs. 16%) for the wider buffer, and, regardless of width, buffer effectiveness increased 0.62% yr. Buffer vegetative type was never statistically significant. In the deep-groundwater depth (2.1-3.5 m), there was no change in NO-N removal over time, although the statistical interaction of width and vegetative type indicated a wide range of removal rates (19-82%). The DOC concentrations were analyzed at the field/buffer and buffer/stream sampling locations. Depending on location position and groundwater sampling depth, DOC concentrations ranged from 1.6 to 2.8 mg L at Year 0 and increased at a rate of 0.13 to 0.18 mg L yr but always remained low (≤5.0 mg L). Greater DOC concentrations in the intermediate-depth groundwater did not increase NO-N removal; redox measurements indicated intermittent reduced soil conditions may have been limiting. This study suggests that riparian buffer width, not vegetation, is more important for NO-N removal in the middle coastal plain of North Carolina for a newly established buffer.

Seasonal variation in the quality of dissolved and particulate organic matter exchanged between a salt marsh and its adjacent estuary

Fluorescence was used to examine the quality of dissolved and particulate organic matter (DOM and POM) exchanging between a tidal creek in a created salt marsh and its adjacent estuary in eastern North Carolina, USA. Samples from the creek were collected hourly over four tidal cycles in May, July, August, and October 2011. Absorbance and fluorescence of chromophoric DOM (CDOM) and of base-extracted POM (BEPOM) served as the tracers for organic matter quality while dissolved organic carbon (DOC) and base-extracted particulate organic carbon (BEPOC) were used to compute fluxes. Fluorescence was modeled using parallel factor analysis (PARAFAC) and principle components analysis (PCA) of the PARAFAC results. Of nine PARAFAC components (C) modeled, C3 represented recalcitrant DOM and C4 represented fresher soil-derived source DOM. Component 1 represented detrital POM, and C6 represented planktonic POM. Based on mass balance, recalcitrant DOC export was 86 g C m−2 yr−1 and labile DOC export was 49 g C m−2 yr−1; no planktonic DOC was exported. The marsh also exported 41 g C m−2 yr−1 of detrital terrestrial POC, which likely originated from lands adjacent to the North River estuary. Planktonic POC export from the marsh was 6 g C m−2 yr−1. Assuming the exported organic matter was oxidized to CO2 and scaled up to global salt marsh area, respiration of salt marsh DOC and POC transported to estuaries could amount to a global CO2 flux of 11 Tg C yr−1, roughly 4% of the recently estimated CO2 release for marshes and estuaries globally.

Shallow Subsurface Drains to Reduce Nitrate Losses from Drained Agricultural Lands

Data was collected between January 2001-September 2002 from two drainage systems near Plymouth, N.C. to evaluate the effect of subsurface drain depth on nitrate-nitrogen (NO3 --N) losses. Drains in Plot 1 were 1.5 m deep and 25 m apart, and drains in Plot 2 were 0.75 m deep and 12.5 m apart. Both plots received swine wastewater applications. Overall, decreased drain depth reduced drainage outflows by 42%. Lower NO3 --N concentrations were observed in the shallow groundwater beneath the shallow drainage plots as a result of higher water tables and increased denitrification. However, NO3 --N concentrations in the drainage water from the shallow drains were not reduced. On average, NO3 --N export from the shallow subsurface drains was 8 kg/ha in 2001 and 27 kg/ha in 2002. Nitrate export from the deeper drains was 6 kg/ha in 2001 and 37 kg/ha in 2002. Overall, an average of 8 kg/ha less NO3 --N was exported from the shallow subsurface drainage system. Decreased export observed in 2002 from the shallow subsurface drainage system was significant at the 10% level, but not for the entire 21-month period.

Calibration of the INCA-N Model in the Pyhäjoki and Yläneenjoki Catchments in Finland

Models serve as a method of gaining an understanding of nutrient processes occurring in natural systems and testing scenarios on how to cost effectively reduce nutrient loading. The Integrated Catchment model for Nitrogen (INCA-N) was applied to the catchments of the River Ylaneenjoki (233 km2) and the River Pyhajoki (78 km2) to improve the estimations of nitrogen load reaching Lake Pyhajarvi in south-western Finland. The model was calibrated for flow, nitrate concentrations, and ammonium concentrations for each catchment for the years 2003-2008. The simulated hydrograph was similar to the observed hydrograph in each catchment with the major difference being the flow peaks were lower in the simulated results (R2=0.71-0.72). The dynamics of nitrate concentrations were reasonably represented in each catchment, but the extreme observed values in summer and winter were not reproduced in the simulations (R2=0.37-0.46). The simulated ammonium concentrations followed the seasonal trends of the observed data based on visual inspection, but statistically were not as good as the flow or nitrate calibrations (R2=0.20-0.25). In the Ylaneenjoki catchment, the simulated ammonium concentrations are much lower than the observed concentrations in the summer. For the Pyhajoki catchment, the simulated spring and winter peaks in ammonium were higher than the observed data in all years except 2003. The results support the need for accurate inputs to the model, especially fertilizer application rates. The calibrations also showed that continuous nutrient monitoring data is beneficial for producing accurate watershed models.