David F. Spencer

Field Evaluation of Degree-Day Based Equations for Predicting Sprouting of Hydrilla (Hydrilla verticillata) Turions and Tubers

ABSTRACT The ability to predict sprouting of aquatic macrophyte vegetative propagules is an important step in understanding their temporal distribution and abundance and in developing long-range management strategies. We examined the ability of degree-day based equations to predict monoecious hydrilla (Hydrilla verticillata L. f. Royle) tuber and turion sprouting in Clear Lake, California using sediment and water temperatures measured in the lake. Sediment temperature data were used to calculate accumulated degree-days. Sprouting of turions and tubers was estimated using previously developed equations relating sprouting to accumulated degree-days. There was good agreement between sprouting predictions and field data on the presence of hydrilla in weed rake samples. Small differences among water temperatures at the five sites and strong relationships between water and sediment temperatures indicate that sprouting should be similar in hydrilla beds found along the western and southern shores of upper Clear Lake. These results can be used to estimate optimal timing for surveys of hydrilla abundance and the application of hydrilla management techniques.

Phenolic Acids and Nutrient Content for Aquatic Macrophytes from Fall River, California

Abstract We compared seasonal changes in tissue C, tissue N, C:N ratio, and total phenolic acids for five species of submersed plants from Fall River, California. Mean tissue C differed among the five species and was between 35 and 40%, except for Ranunculus aquatilis, which was 26%. Mean tissue N differed among species; Ranunculus aquatilis had the lowest mean value (2.71%) and Zannichellia palustris had the highest (3.74%). Mean C:N ratio was between 9.7 and 12.7. Among the five species examined, mean phenolic acid content was greatest for Myriophyllum sibiricum and it was nearly seven times that for the species with the lowest phenolic acid content, Elodea canadensis. Regression analysis indicated positive relationships between phenolic acid content and tissue C for two species, Callitriche hermaphroditica and Ranunculus aquatilis. Regression equations relating phenolic acid content to tissue N were not statistically significant. For Elodea canadensis, the equation describing phenolic acid content as a...

Spatial and Temporal Variation in the Composition and Biomass of Algae Present in Selected California Rice Fields

ABSTRACT We sampled eight California rice fields every two days from May 1 to June 1, 2004 for algal biomass, species composition, and water quality parameters. Soil samples were collected prior to filling the fields with water and analyzed for selected nutrients. Algal abundance shifted from dominance by genera of green algae (Sphaeroplea, Tribonema, Ankistrodesmus, Tetraspora) and diatoms (Navicula) early in May to dominance by blue-green algae genera (almost totally Nostoc, with Anabaena and Phormidium also present) in late May-early June The same taxa occurred in all the fields at around the same time. The most abundant species consistent with the description “black algae” collected from these fields was Nostoc spongiaeforme. Results from multiple regression analysis showed that algal biomass was negatively related to total alkalinity and sulfate concentration, and positively related to the N: P ratio and the concentrations of ammonium, phosphate, sodium, and calcium. These variables explained 51% of the variance associated with total algal biomass. When soil characteristics were used in a similar multiple regression analysis, none of them was significantly (P > 0.1) related to total algal biomass.

Influence of a non-copper algicide on the cyanobacterium, Nostoc spongiaeforme, and the green alga, Hydrodictyon reticulatum, in field and laboratory experiments

Cyanobacteria and algae grow in California rice fields where they form large mats that may smother seedlings or cause them to dislodge, resulting in reduced rice stand establishment and potential yield loss. The most troublesome species of cyanobacteria is Nostoc spongiaeforme. It is very difficult to control using currently accepted methods, i.e., aerial applications of copper sulfate. A non-copper algicide, the mono (N,N-dimethylalkylamine) salt of endothall has been suggested as an alternative method for controlling nuisance cyanobacterial and algal growths in California rice fields. The purpose of the experiments described here was to evaluate the effect of the mono (N,N-dimethylalkylamine) salt of endothall on growth of N.xa0spongiaeforme and the green alga, Hydrodictyon reticulatum. In laboratory experiments, the mono (N,N-dimethylalkylamine) salt of endothall reduced N.xa0spongiaeforme growth at 0.3xa0mgxa0L−1. This effect was removed when rice straw was added to the growth medium, indicating that the rice straw may have introduced bacteria capable of degrading the mono (N,N-dimethylalkylamine) salt of endothall. In outdoor experiments, which used rice field water containing decomposing rice straw, the mono (N,N-dimethylalkylamine) salt of endothall concentrations between 0 and 5xa0mgxa0L−1 had little effect on N. spongiaeforme. In contrast, H. reticulatum exhibited injury symptoms at 1xa0mgxa0L−1 or greater. However, H.xa0reticulatum recovered by the end of the 7-day exposure. It is not clear how this algicide will be useful in the management of N. spongiaeforme or H. reticulatum in California rice fields.

Root Size and Depth Distributions for Three Species of Submersed Aquatic Plants Grown Alone or in Mixtures: Evidence for Nutrient Competition

ABSTRACT We hypothesized that if aquatic plants were competing for nutrients then the spatial distribution and sizes of roots should change when competitors were present. Stukenia pectinatus, Potamogeton nodosus, and Hydrilla verticillata (monoecious type) were grown in either monocultures or mixtures in polyvinylchloride containers. Four 5 cm diameter minirhizotrons were mounted horizontally across the containers so that they were 2.5, 12.5, 22.5, or 32.5 cm below the surface of the sediment, and we inserted a specialized video camera in each minirhizotron tube and recorded root images at 21 locations in each tube. For two of three cases, adding plants of another species changed the root depth distribution and increased the volume of soil occupied by roots compared to monocultures. Additionally, smaller diameter roots were more abundant when competitors were present. This implies that the plants adjusted to the presence of competitors by producing more roots capable of nutrient uptake. These results imply that competition for sediment-based nutrients occurred in these systems.

Nutrient Limitation of Zannichellia palustris and Elodea canadensis Growing in Sediments from Fall River, California

ABSTRACT Predicting aquatic plant growth based on sediment nutrients is problematic. Two experiments with sandy or silty sediments from Fall River, California were performed to identify the limiting nutrient for two abundant species of submersed plants in the river. Growth of Zannichellia palustris L. or Elodea canadensis Rich, was significantly enhanced by the addition of N or a combination of N and P to sandy sediments but not those that were silty. Root shoot ratios declined for plants growing with added nutrients. Plant tissue N concentrations increased as well. Tissue N:P ratios indicated that N rather than P limited growth. Results support the literature hypothesis that sediment N availability may limit growth and distribution of submersed rooted aquatic plants.

Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications

In California’s water-seeded rice systems, algal/cyanobacterial biomass can be a problem during rice establishment and can lead to yield reductions. Laboratory, enclosure, and field-scale experiments were established to evaluate the effects of fertilizer P management on algal/cyanobacterial growth. Two field-scale experiments evaluated the response of algal/cyanobacterial growth to three P management strategies: conventional surface applied, incorporated into the soil, and delaying P applications by 30xa0days. Results from these experiments indicated rice fields that received conventional surface-applied P fertilizer had 4–8 times more algal/cyanobacterial biomass and 3–11 times higher concentrations of soluble reactive phosphate (SRP) than those in which P fertilizer was incorporated or delayed. Laboratory experiments evaluated the ability of field water to support growth of Nostoc spongiaeforme. Results indicate that water from the incorporated or delayed P application fields was P limited for N. spongiaeforme growth. Water from the surface-applied fields was not P limited. Enclosure experiments evaluated the effects of delayed P applications on algal/cyanobacterial biomass and rice yields. Algal/cyanobacterial cover and biomass increased in enclosures which received added P. Soluble reactive phosphate concentrations were also significantly greater in these enclosures. Delaying the application by up to 28xa0days did not reduce rice yields in the enclosures. One management implication is that reducing SRP concentrations early in the season in rice field water will result in reduced algal/cyanobacterial biomass. Strategies to reduce water SRP include incorporating fertilizer P or delaying the P application by up to 30xa0days.

Response of Arundo donax L. (giant reed) to leaf damage and partial defoliation

Arundo donax (giant reed) is a tall clonal invasive grass which has impacted many riparian ecosystems in the US. Experiments tested the hypotheses (1) that defoliation would affect A. donax stem growth and leaf production and (2) that leaf damage or removal would influence A. donax photosynthetic rates using a combination of field and laboratory settings. Leaf defoliation did not affect the height of stems or the number of leaves per stem for plants growing at a field site. Leaf damage did not influence the electron transport rate (ETR) for damaged or adjacent leaves, and defoliated stems maintained ETR which were similar to those of undamaged leaves. These findings suggest that moderate to low levels of leaf damage and/or defoliation alone may not significantly influence growth of A. donax stems and leaves and, therefore, may not reduce A. donax persistence in a particular habitat. Further, these results provide a benchmark against which to judge the effects of management approaches which affect A. donax shoots.

An evaluation of flooding risks associated with giant reed (Arundo donax)

The presence of vegetation in a channel may influence water movement in the channel and the surrounding land in several ways. One hypothesis is that increased abundance of the invasive plant Arundo donax in a watercourse contributes to increased flooding risk. To test this hypothesis, we determined Mannings coefficient for A. donax and subsequently used it in the HEC-RAS model to estimate the impact that A. donax has on flooding risks at three sites within two moderately sized northern California rivers. The mean value for Mannings coefficient for A. donax was 0.066, and it varied from 0.019 to 0.121 (n = 37). Model simulations showed that A. donax within a stream channel had a direct effect on flooded area, causing increases up to 10% above baseline conditions, which represent cross sections with no A. donax present. Storm size also affected A. donaxs impact on the size of the flooded area. Using the maximum value for Mannings n for A. donax in the simulations resulted in an increase in the flooded area from 10% to 19% compared to simulations in which there was no A. donax present. Impacts of A. donax on other stream systems could differ, but they can be estimated using the value for Mannings n for A. donax provided in this study. This information can be used in conjunction with natural resource conditions, such as soil type, to prioritize areas for A. donax management.