Rio de Dios

Lost Links and Empty Aquifers

24 losT links and empTy aquiFers The connectedness derived fromVannote’s river continuum concept,linking the flow headwater to estuary,is shattered here,replaced instead by a homogeneous and prosthetic artifice that is hostile to most life, rather than the stratigraphic ballet of sorted aquatic insect and fish groups as one descends a natural stream. In a pristine stream system, the headwaters are characterized by dense overshading riparian vegetation that sheds leaves and organic debris (coarse particulate organic matter, or CPOM) into the nutrient-poor (oligotrophic), clear headwaters. This organic material can form as much as 90% of the energy moving through a lotic (flowing) system, and the headwater reaches are dominated by aquatic insects whose mouth parts are specialized to shred leaves (“shredders”), as well as some predators and collectors that filter small, fine particulate organic matter (FPOM) from the water column.The middle section of the stream is wider, has some nutrients in the water, and sunlight can penetrate the water column to the bottom, stimulating algal and aquatic weed growth. In this middle reach area of the stream, a group of scraping and grazing specialists (“grazers”) scour the benthic (bottom) environment, eating algal films and plants, and there is a strong presence of collectors harvesting the FPOM drifting downstream from the headwaters. In the lowest reaches of the idealized river, there is nothing to graze upon because the murkiness of the water prevents sunlight from penetrating to the bottom, and there is no CPOM, thus collectors dominate. Predators are a minor component of each of the three stream sections.Table 2 summarizes these points (pp. 26–27). 25 This description shows how it should be—and for thousands of years, how it was. Now it’s different of course. Despite tiny fragments of a healthy headwater setting,the middle and lowest reaches of the LosAngeles River have been sacrificed. As Jenny Price recently noted,“The cement channel . . . constitutes L.A.’s strategy to move storm water,that life-giving natural resource,through the city.A city with a semi-arid Mediterranean climate pours as much rainwater (which we get from the sky for free) as possible into the storm sewers, through the river, and into the Pacific—and then pays dearly to import water by aqueduct from up to 400 miles away. Call it watering the ocean, by draining watersheds across the West” (Price, 2007). The U.S.Army Corps of Engineers and the Los Angeles County Department of Public Works, who periodically clear sediment and the struggling vegetation to maintain flood control capacity,operate the channelized river course itself.The riverbed is principally sand with surficial silts.The river’s water quality is highly impaired,and does not meet existing standards for pH,AMM,lead,coliform,trash, scum algae, total dissolved solids, and turbidity. It’s hard to know what to do with realities such as these. Just because we have heard it before does not make it any less true.What response is appropriate? How does one sort out these facts? Writing as a father, teacher, ecologist, and lover of the natural world,I often search for metaphors to explain basic ideas such as these, following the theory that an image is worth a thousand smolts.To illustrate the impoverishment of hard-bottom channels to my freshwater biology classes, I use slides of the channelized Los Angeles River and present it as a sort of open tomb 26 exhibit—a grave from which the native species have long been raptured. Seeing the pictures, it is starkly obvious that it didn’t have to be this way, and that nature (and natural wisdom) has come in pretty close to last place. •฀฀Stream฀Order฀1-3฀(0.5฀-฀6฀meters)—small,฀narrow฀stream •฀฀dense฀riparian฀vegetation •฀฀closed฀canopy—shady,฀light฀limited •฀฀cold,฀constant฀water฀temperature฀(spring-like;฀oligotrophic);฀clear •฀฀gravel฀bottom;฀erosion฀zone฀of฀the฀stream •฀฀heavy฀litter฀load฀and฀abundant฀coarse฀particulate฀organic฀matter฀(CPOM) •฀฀high฀gradient,฀usually฀with฀steep฀valley฀sides;฀sediment฀shedding฀area฀of฀the฀stream •฀฀mostly฀riffle฀habitat;฀high฀in฀elevation฀(rapid฀drop฀in฀elevation) •฀฀low฀aquatic฀primary฀productivity—secondary฀producers฀feed฀on฀CPOM •฀฀Productivity/Respiration฀ratio฀(P/R1) •฀฀200-500฀species฀of฀invertebrates Table 2 (continued) condiTions in The mid-reach oF The river: loWermosT secTions—noT presenT in The modern l.a. river sysTem: 28 Table 3...