Sampling and Mapping a Soil Erosion Cover Factor by Integrating Stratification,Model Updating and Cokriging with Images

Cost-efficient sample designs for collection of ground data and accurate mapping of variables are required to monitor natural resources and environmental and ecological systems. In this study, a sample design and mapping method was developed by integrating stratification, model updating, and cokriging with Landsat Thematic Mapper (TM) imagery. This method is based on the spatial autocorrelation of variables and the spatial cross-correlation among them. It can lead to sample designs with variable grid spacing, where sampling distances between plots vary depending on spatial variability of the variables from location to location. This has potential cost-efficiencies in terms of sample design and mapping. This method is also applicable for mapping in the case in which no ground data can be collected in some parts of a study area because of the high cost. The method was validated in a case study in which a ground and vegetation cover factor was sampled and mapped for monitoring soil erosion. The results showed that when the sample obtained with three strata using the developed method was used for sampling and mapping the cover factor, the sampling cost was greatly decreased, although the error of the map was slightly increased compared to that without stratification; that is, the sample cost-efficiency quantified by the product of cost and error was greatly increased. The increase of cost-efficiency was more obvious when the cover factor values of the plots within the no-significant-change stratum were updated by a model developed using the previous observations instead of remeasuring them in the field.     

Creating False Images: Stream Restoration in an Urban Setting

Stream restoration has become a multibillion dollar business with mixed results as to its efficacy. This case study utilizes pre‐ and post‐monitoring data from restoration projects on an urban stream to assess how well stream conditions, publicly stated project goals, and project implementation align. Our research confirms previous studies showing little communication among academic researchers and restoration practitioners as well as provides further evidence that restoration efforts tend to focus on small‐scale, specific sites without considering broader land use patterns. This study advances our understanding of restoration by documenting that although improving ecological conditions is a stated goal for restoration projects, the implemented measures are not always focused on those issues that are the most ecologically salient. What these projects have accomplished is to protect the built environment and promote positive public perception. We argue that these disconnects among publicized goals for restoration, the implemented features, and actual stream conditions may create a false image of what an ecologically stable stream looks like and therefore perpetuate a false sense of optimism about the feasibility of restoring urban streams.     

Assimilation of symbiont-derived photosynthates in some solitary and colonial radiolaria

Evidence for host assimilation of ¹⁴C-labeled symbiont photosynthates is presented from laboratory studies of the solitary radiolarian Thalassicolla nucleata and the colonial species Collosphaera huxleyi. The amount of ¹⁴C-labeled product assimilated in the central capsule of T. nucleata is directly related to the amount of ¹⁴C incorporated by the symbionts. In C. huxleyi central capsules, the percentage of ¹⁴C-label occurring in the water-soluble fraction is 38% and in the lipid-soluble fraction is 20%, the remainder being in insoluble products. Within the lipid-soluble fraction, a substantial percentage of the ¹⁴C activity is associated with the triglyceride and wax ester fractions. The significance of these findings is discussed in relation to the possible physiological role of symbionts in sustaining the host and stabilizing the host-symbiont association.     

Sediment preferences and oil contamination in the Pacific sand lance Ammodytes hexapterus

Sand lance, Ammodytes hexapterus Pallas, forage for zooplankton in the water column and are under heavy predation from fish, marine birds and marine mammals. To avoid predation, these fish bury themselves in soft bottom sediments when not foraging and during overwintering. We collected sand lance in Sequim Bay, Washington State, USA, in 1982. In three experiments we presented the fish with: (1) four different sediment types (fine sand, coarse sand, gravel, silt) to determine their sediment preferences; (2) clean and oil-contaminated preferred sediment to determine whether the fish would avoid the contamination; and (3) clean unpreferred and oil-contaminated preferred sediment to determine whether the contamination would alter their sediment preferences. In the first experiment, sand lance preferred to bury in fine and coarse sands and avoided gravel and silt. In the second experiment, sand lance avoided sand contaminated with Prudhoe Bay crude oil (116 and 1050 ppm). In the third experiment, sand lance avoided the oiled sand (131 and 1041 ppm) and buried in clean gravel, and also avoided both oiled sand (113 and 1004 ppm) and clean silt, and chose to remain in the water column. The sediment particle size and the way it affects water flow through the sediment seemed to be responsible for the preferences. We suggest that the sediment type, the sediment distribution, the nutritional state of the fish, and the predation pressure influence how sand lance use the sediment as a refuge and how they respond to contamination of that refuge.Contribution No. 1392 of the School of Oceanography, University of Washington     

Mercury volatilisation and phytoextraction from base-metal mine tailings

Experiments were carried out in plant growth chambers and in the field to investigate plant-mercury accumulation and volatilisation in the presence of thiosulphate (S2O3)-containing solutions. Brassica juncea (Indian mustard) plants grown in Hg-contaminated Tui mine tailings (New Zealand) were enclosed in gastight volatilisation chambers to investigate the effect of ammonium thiosulphate ([NH4]2 S2O3) on the plant-Hg volatilisation process. Application of (NH4)2 S2O3 to substrates increased up to 6 times the Hg concentration in shoots and roots of B. juncea relative to controls. Volatilisation rates were significantly higher in plants irrigated only with water (control) when compared to plants treated with (NH4)2 S2O3. Volatilisation from barren pots (without plants) indicated that Hg in tailings is subject to biological and photochemical reactions. Addition of sodium thiosulphate (Na2S2O3) at 5 g/kg of substrate to B. juncea plants grown at the Tui mine site confirmed the plant growth chambers studies showing the effectiveness of thio-solutions at enhancing shoot Hg concentrations. Mercury extraction from the field plots yielded a maximum value of 25 g/ha. Mass balance studies revealed that volatilisation is a dominant pathway for Hg removal from the Tui mine site. A preliminary assessment of the risks of volatilisation indicated that enhanced Hg emissions by plants would not harm the local population and the regional environment.