Kathleen A. Dwire

Mechanisms of carbon storage in mountainous headwater rivers

Published research emphasizes rapid downstream export of terrestrial carbon from mountainous headwater rivers, but little work focuses on mechanisms that create carbon storage along these rivers, or on the volume of carbon storage. Here we estimate organic carbon stored in diverse valley types of headwater rivers in Rocky Mountain National Park, CO, USA. We show that low-gradient, broad valley bottoms with old-growth forest or active beaver colonies store the great majority of above- and below-ground carbon. These laterally unconfined valley segments constitute <25% of total river length, but store ∼75% of the carbon. Floodplain sediment and coarse wood dominate carbon storage. Our estimates of riverine carbon storage represent a previously undocumented but important carbon sink. Our results indicate that: not all mountainous rivers rapidly export carbon; not all valley segments are equally important in carbon storage; and historical changes in riverine complexity have likely reduced carbon storage.

Floristic comparison of freshwater wetlands in an urbanizing environment

We evaluated the floristic condition of freshwater palustrine wetlands dominated by wet meadow, emergent marsh, aquatic vegetation, or open water within the rapidly urbanizing area of Portland, Oregon, USA by (1) characterizing plant species richness (presence/absence) and composition of naturally occurring wetlands (NOWs) and mitigation wetlands (MWs) and (2) identifying relationships between floristic characteristics and variables describing land-use, site conditions, and mitigation activities. Data were collected on 45 NOWs and 51 MWs. Overall species richness was high (365 plant taxa), but more than 50% of the species present on both NOWs and MWs were introduced. Only 14 species occurred on more than half the sites, and nine of them were invasive introduced species. The mean number of native species per site did not differ between land-use categories (ANOVA, F=0.62 at 3 and 88 df, p=0.6031); however, wetlands surrounded by agricultural and commercial/industrial/transportation corridor uses had more introduced species per site than wetlands surrounded by undeveloped land (Fishers Protected LSD at 88 df, p ≤ 0.05). Although overlapping in floristic composition. NOWs and MWs had significantly different (MRPP, p < 0.0001) species assemblages that were identified using TWINSPAN. MRPP analyses for all sites showed that watershed, land-use, HGM class, percent cover of water, and MW age were significantly related to the floristic composition of the study wetlands. Canonical correspondence analyses further revealed that the primary gradient for species distribution in NOWs was related to moisture; the secondary gradient was related to land-use. The primary gradient also described a strong relationship between percent cover of water and HGM class. For MWs, the primary gradient was related to watershed location and surrounding landuse; the secondary gradient was related to percent cover of water and MW age. Most MWs (44 out or 51 sites) were depressions in various settings, so while HGM class separates NOWs from MWs, it does little to distinguish MW assemblages. Our results show that wetlands in the urbanizing study area are floristically degraded. Further, current wetland management practices are replacing natural marsh and wet meadow systems with ponds, resulting in changes in the composition of plant species assemblages.

Age structure and age-related performance of sulfur cinquefoil (Potentilla recta)

Abstract Age distributions of sulfur cinquefoil populations were determined on sites that were historically grazed, cultivated, and mechanically disturbed. From 12 sites, a total of 279 reproductively active plants were collected and aged by using herbchronology (counting rings in the secondary root xylem of the root crown) to (1) estimate the age structure of the populations, (2) relate plant size and flower production to plant age, and (3) examine the relation of population age structure to environmental variables and disturbance history. Results indicated that the mean age for all sampled plants was 3.5 (± 1.74 SD) yr and ranged from 1 to 10 yr. Age was not related to number of flowers, plant size (number of stems per plant or plant height), or site disturbance type but was positively correlated with site elevation (P < 0.001). The pooled age distribution from all 12 sites was right-skewed with fewer old plants than young plants. We conclude that sulfur cinquefoil plants sampled in northeast Oregon are able to colonize, establish, and reproduce at disturbed sites rapidly. We suggest that herbchronology may be a useful technique to improve understanding of invasion biology and ecology for invasive plant species that form annual rings. Nomenclature: Sulfur cinquefoil, Potentilla recta L. PTLRC.

Seed Production and Dispersal of Sulfur Cinquefoil in Northeast Oregon

Abstract Sulfur cinquefoil (family Rosaceae) is an invasive, herbaceous perennial, native to Eurasia. It has wide ecological amplitude and has become established throughout North America in numerous habitat types. Sulfur cinquefoil reproduces only by seed (achenes); however, little is known about its regenerative strategy or reproductive biology. To improve understanding of the mechanisms of expansion for sulfur cinquefoil, we quantified seed production and measured seed dispersal at sites infested with sulfur cinquefoil in different habitats in northeast Oregon. Seed dispersal was measured by using sticky traps (30 × 100 cm, replaced every 2 weeks) radiating in 4 cardinal directions from individual source plants. Estimated seed production for 2 years (2001 and 2002) was nearly 4 times higher than previously reported (≈6 000 seeds per plant; range ≈ 2 620–15 150 seeds per plant). For most sites, seed production was similar in both years. However, site, year, and their interaction (site × year) had significant influence on flower and stem production. Seeds were dispersed from July through mid-October 2001, although almost 40% of the seeds were captured between mid-July and mid-August. Dispersal followed a classic decay function; approximately 83% of the seeds were captured within 60 cm of the source plants. Once sulfur cinquefoil reaches a site, it appears to spread and persist by releasing numerous seeds near the parent plants, thereby forming increasingly dense stands.

Influence of Bedrock Geology on Water Chemistry of Slope Wetlands and Headwater Streams in the Southern Rocky Mountains

We characterized the water chemistry of nine slope wetlands and adjacent headwater streams in Colorado subalpine forests and compared sites in basins formed on crystalline bedrock with those formed in basins with a mixture of crystalline and sedimentary bedrock. The pH, Ca2+, Mg2+, NH4+, acid neutralizing capacity, and electrical conductivity of wetland porewater and streamwater were higher in the basins with mixed geology. Bryophyte cover was higher in lower pH, crystalline basins, and vascular plant cover was higher in the mixed bedrock basins. On average, wetland porewater had lower pH and higher concentrations of dissolved organic carbon (DOC) and nitrogen and several other ions than streamwater; however, because discharge from these small wetlands is low, their direct influence on stream solute concentrations was generally undetectable. Dilution altered stream solute concentrations during peak flow in both basin types, but had little effect on wetland chemistry. In contrast to other solutes, the concentration of DOC in streams increased marginally during peak runoff and its concentration in wetland porewater was stable throughout the year. These findings further knowledge of the influence of watershed characteristics on wetland and stream chemistry and will inform future decisions regarding conservation and management in headwater basins.