Mercury inputs and redistribution in the Penobscot River and estuary, Maine.

We examined total mercury (Hg) distributions in sediments from the Penobscot River and estuary, Maine, a site of extensive Hg releases from HoltraChem (1967-2000). Our objectives were to quantify: (1) bottom sediment Hg inventories (upper ~1m; 50-100 y); (2) sediment accumulation rates; and (3) contemporary Hg fluxes to bottom sediments; by sampling the Penobscot River (PBR), Mendall Marsh (MM), the Orland River (OR) and the Penobscot estuary (ES). Hg was rapidly distributed here, and the cumulative total (9.28 metric tons) associated with sediments system-wide was within the range released (6-12 metric tons). Evidence of sediment/Hg remobilization was observed in cores primarily from the PBR, and to a lesser extent the ES, whereas cores from MM, most of the OR, the ES, and half from the PBR exhibited sharp peaks in Hg concentrations at depth, followed by gradual decreases towards the surface. Based on background PBR sediment Hg concentrations (100ngg-1), "elevated" (300ngg-1), or "highly elevated" (600ngg-1) Hg concentrations in sediments, and resulting inventories, we assessed impact levels ("elevated"≥270, or "highly elevated"≥540mgm-2). 71% of PBR stations had "elevated", and 29% had "highly elevated" Hg inventories; 45% of MM stations had "elevated", and 27% had "highly elevated" inventories; 80% of OR stations had "elevated" inventories only; and 17% of ES stations had "elevated" inventories only. Most "highly elevated" stations were located within 8km of HoltraChem, in MM, in the PBR, and in the OR. Near-surface sediments in the OR, PBR and MM were all "highly elevated", while those in the ES were "elevated", on average. Mean Hg fluxes to bottom sediments were greatest in the OR (554), followed by the PBR (469), then MM (452), and finally the ES (204ngcm-2y-1).

Spatial patterns of grass seedling recruitment imply predation and facilitation by harvester ants.

Extended drought on the Edwards Plateau, TX, causes high mortality in grass species' populations and their replacement by recruitment from the seeds of survivors. Harvester ant nests may act as refugia for perennial plants during drought, as evidenced by a high survivorship of plants directly adjacent to nests. Because grasses tend to disperse seeds short distances and drought eliminated seed banks, we hypothesized that the spatial pattern of grass seedlings and adults would be clumped at small scales around these refugia. In contrast, nests would be regular at small to moderate scales. We studied the spatial patterns of seedlings, adults, and ant nest locations using a modified Ripley's K-function technique for transect data. Point data were collected along a 1-km transect. Spatially regular patterns were found for nests from 1.0- to 22.0-m scales. We found that two species' seedlings and adults were significantly clumped with ant nests, and two species had significantly regular spatial patterns with nests. Surprisingly, patterns of clumped seedlings occurred up to 30-m scales with nests. Nests appear to affect seedling establishment at multiple scales. These results suggest that nests may facilitate colonization for some grass populations, but regular spatial patterns in other species imply that forager seed harvest may inhibit establishment.

Attitudes towards biosecurity practices relevant to Johne's disease control on beef cattle farms.

The success of control programs can be improved when producers' attitudes towards these programs are positive. Implementation of control programs for chronic diseases are more challenging than those for acute diseases because of the absence of the "cues-to-action" that are associated with acute diseases. Johne's disease (JD) is a chronic diarrheal disease of ruminants, and national voluntary control programs exist in several countries. We used a mailed cross-sectional survey to describe the attitudes of producers towards biosecurity practices and veterinarians' beliefs relevant to the control of JD on beef farms. Another objective was to describe and compare the attitudes of producers and veterinarians towards specific measures recommended by the Texas Voluntary Johne's Disease Program (TVJDP) for cattle. Questionnaires were mailed to 1100 producers and 840 veterinarians in the state of Texas, USA. Two hundred and eighty-five producers (26%) and 153 veterinarians (18%) returned questionnaires for analysis. Fifty-nine percent of producers and 50% of veterinarians agreed that JD is responsible for substantial losses in beef cattle production. Sixty-four percent of veterinarians had educated producers on management strategies for the control or elimination of JD. However, only 36% had participated in the training program and 29% were certified to develop risk assessments and implement testing. Only 20% of producers reported that they were familiar with the TVJDP and 16% had considered participating in this program. There is a need for greater promotion of the control program among veterinarians and producers. Reasons for the apparent difference in opinions need to be understood to increase the likelihood of control measures adoption and to subsequently reduce the impact of JD on beef cattle operations.

Benefits of obtaining test-negative Level 4 classification for beef producers in the Voluntary Bovine Johne's Disease Control Program.

The US Voluntary Bovine Johne's Disease Control Program (VBJDCP) stipulates the national standards for Johne's disease (JD) control, and herds classified as test-negative at Level 4 of the VBJDCP have the greatest likelihood of being non-infected. A questionnaire survey of owners of VBJDCP test-negative Level 4 beef herds was conducted to describe perceived benefits of attaining Level 4 status. Thirty-nine of the 40 producers returned completed or partially completed surveys. Sixty-four percent (23/36) of herds contained 50 or less test eligible cattle. Twenty-seven percent (10/37) of producers reported increased marketing opportunities as a goal for enrollment in the VBJDCP. Classification at test-negative Level 4 status in the VBJDCP led to increased marketing opportunities for more than one-third (13/35) of the producers. Twenty-five percent (9/36) of the producers reported significant and 39% (14/36) marginal benefits (financial and non-financial) as a result of participation in the VBJDCP. The median (range) reported annual benefit was $0 ($0, $10,000), whilst the median (range) annual cost of implementing and sustaining the VBJDCP on ranches was $200 ($0, $5000). It is suggested that greater publicity about the VBJDCP in the beef cattle industry will increase its chances of success by increasing awareness amongst producers concerned about herd health/disease monitoring, and through improved marketing opportunities.

Does vegetation prevent wave erosion of salt marsh edges?

This study challenges the paradigm that salt marsh plants prevent lateral wave-induced erosion along wetland edges by binding soil with live roots and clarifies the role of vegetation in protecting the coast. In both laboratory flume studies and controlled field experiments, we show that common salt marsh plants do not significantly mitigate the total amount of erosion along a wetland edge. We found that the soil type is the primary variable that influences the lateral erosion rate and although plants do not directly reduce wetland edge erosion, they may do so indirectly via modification of soil parameters. We conclude that coastal vegetation is best-suited to modify and control sedimentary dynamics in response to gradual phenomena like sea-level rise or tidal forces, but is less well-suited to resist punctuated disturbances at the seaward margin of salt marshes, specifically breaking waves.