Geology topics

Research about Fanno Creek

Source-linked reports with geographic coverage including Fanno Creek.

5 recordsLinked to original sources

USGS2015

Organic matters: Investigating the sources, transport, and fate of organic matter in Fanno Creek, Oregon

The term organic matter refers to the remnants of all living material. This can include fallen leaves, yard waste, animal waste, downed timber, or the remains of any other plant and animal life. Organic matter is abundant both on land and in water. Investigating organic matter is necessary for understanding the fate and transport of carbon (a major constituent of organic matter). Organic matter is necessary for maintaining a healthy ecosystem. It participates in a wide range of ecological functions, such as supplying food to the microbes that are part of the foundation of the food chain. Organic matter also plays a role in many other natural functions, including the binding and transport of some trace metals and controlling how light is absorbed in the water column. Organic matter in a stream can be found in many places, such as in the leaves that have fallen from a tree (termed "leaf litter"), in algae floating in the stream or attached to rocks, as part of the soil, or even suspended or dissolved in the water. The U.S. Geological Survey (USGS), in cooperation with Clean Water Services, recently completed an investigation into the sources, transport, and fate of organic matter in the Fanno Creek watershed. The information provided by this investigation will help resource managers to implement strategies aimed at decreasing the excess supply of organic matter that contributes to low dissolved-oxygen levels in Fanno Creek and downstream in the Tualatin River during summer. This fact sheet summarizes the findings of the investigation.

Oregon↗

USGS2014

Investigating organic matter in Fanno Creek, Oregon, Part 1 of 3: estimating annual foliar biomass for a deciduous-dominant urban riparian corridor

For this study, we explored the amount, type, and distribution of foliar biomass that is deposited annually as leaf litter to Fanno Creek and its floodplain in Portland, Oregon, USA. Organic matter is a significant contributor to the decreased dissolved oxygen concentrations observed in Fanno Creek each year and leaf litter is amongst the largest sources of organic matter to the stream channel and floodplain. Using a combination of field measurements and light detection and ranging (LiDAR) point cloud data, the annual foliar biomass was estimated for 13 stream reaches along the creek. Biomass estimates were divided into two sets: (1) the annual foliage available from the entire floodplain overstory canopy, and (2) the annual foliage overhanging the stream, which likely contributes leaf litter directly to the creek each year. Based on these computations, an estimated 991 (±22%) metric tons (tonnes, t) of foliar biomass is produced annually above the floodplain, with about 136 t (±24%) of that foliage falling directly into Fanno Creek. The distribution of foliar biomass varies by reach, with between 150 and 640 t/km2 produced along the floodplain and between 400 and 1100 t/km2 available over the channel. Biomass estimates vary by reach based primarily on the density of tree cover, with forest-dominant reaches containing more mature deciduous trees with broader tree canopies than either wetland or urban-dominant reaches, thus supplying more organic material to the creek. By quantifying the foliar biomass along Fanno Creek we have provided a reach-scale assessment of terrestrial organic matter loading, thereby providing land managers useful information for planning future restoration efforts.

Oregon↗

USGS2014

Investigating organic matter in Fanno Creek, Oregon, Part 2 of 3: sources, sinks, and transport of organic matter with fine sediment

Organic matter (OM) is abundant in Fanno Creek, Oregon, USA, and has been tied to a variety of water-quality concerns, including periods of low dissolved oxygen downstream in the Tualatin River, Oregon. The key sources of OM in Fanno Creek and other Tualatin River tributaries have not been fully identified, although isotopic analyses from previous studies indicated a predominantly terrestrial source. This study investigates the role of fine sediment erosion and deposition (mechanisms and spatial patterns) in relation to OM transport. Geomorphic mapping within the Fanno Creek floodplain shows that a large portion (approximately 70%) of the banks are eroding or subject to erosion, likely as a result of the imbalance caused by anthropogenic alteration. Field measurements of long- and short-term bank erosion average 4.2 cm/year and average measurements of deposition for the watershed are 4.8 cm/year. The balance between average annual erosion and deposition indicates an export of 3,250 metric tons (tonnes, t) of fine sediment to the Tualatin River—about twice the average annual export of 1,880 t of sediment at a location 2.4 km from the creek’s mouth calculated from suspended sediment load regressions from continuous turbidity data and suspended sediment samples. Carbon content from field samples of bank material, combined with fine sediment export rates, indicates that about 29–67 t of carbon, or about 49–116 t of OM, from bank sediment may be exported to the Tualatin River from Fanno Creek annually, an estimate that is a lower bound because it does not account for the mass wasting of organic-rich O and A soil horizons that enter the stream.

Oregon↗

USGS2014

Investigating organic matter in Fanno Creek, Oregon, Part 3 of 3: identifying and quantifying sources of organic matter to an urban stream

The sources, transport, and characteristics of organic matter (OM) in Fanno Creek, an urban stream in northwest Oregon, were assessed and quantified using: (1) optical instruments to calculate transported loads of dissolved, particulate, and total organic carbon, (2) fluorescence spectroscopy and stable isotope ratios (δ 13 C, δ 15 N) to elucidate sources and chemical properties of OM throughout the basin, and (3) synoptic sampling to investigate seasonal and hydrologic variations in the characteristics and quantity of OM. Results from this study indicate that of the roughly 324 (±2.9%) metric tons (tonnes, t) of organic carbon exported from the basin during March 2012 to March 2013, most of the OM in Fanno Creek was dissolved (72%) and was present year-round at concentrations exceeding 3–4 milligrams of carbon per liter, whereas particulate carbon typically was mobilized and transported only by higher-flow conditions. The isotopic and fluorescence characteristics of Fanno Creek OM indicate that the carbon originates primarily from terrestrial inputs, most likely riparian vegetative biomass that enters the stream via litterfall and overland transport and then travels through the system episodically as a result of hydrologic processes. The amount of OM exported from the Fanno Creek drainage over the course of a year in this study is consistent with previous estimates of annual riparian litterfall in or near the creek. Although the creek channel is actively eroding, most bank material has too little OM for that to be a dominant source of OM to the stream. Fluorescence data revealed that the OM contains primarily humic and fulvic-like components that become less aromatic as the OM moves downstream. The most significant seasonal variation was associated with OM transported in the first storms of the autumn season (fall flush). That material was characteristically different, with a larger fraction of microbially derived OM that probably resulted from an accumulation of easy-to-mobilize and decomposing material in the streambed during previous months of summertime low-flow conditions. The first fall flush produced the highest concentrations of OM of the entire year, and the resulting load of mobilized and decomposing OM resulted in a significant oxygen demand immediately downstream in the Tualatin River.

Oregon↗

USGS2011

Normalized Difference Vegetation Index for Fanno Creek, Oregon

Fanno Creek is a tributary to the Tualatin River and flows though parts of the southwest Portland metropolitan area. The stream is heavily influenced by urban runoff and shows characteristic flashy streamflow and poor water quality commonly associated with urban streams. This data set represents the Normalized Difference Vegetation Index (NDVI), or "greenness" of the Fanno Creek floodplain study area. Aerial photography was used to isolate areas of vegetation based on comparing different bandwidths within the imagery. In this case, the NDVI is calculated as the quotient of the near infrared band minus the red band divided by the near infared plus the red band. NDVI = (NIR - R)/(NIR + R).

Oregon↗