Do we focus too much on flows Do we focus too much on flows? Colorado River Water Users Association December 13, 2017 Charles B. Yackulic (U.S.Geological Survey – GCMRC) email: cyackulic@usgs.gov With lots of help from Bridget Deemer, Kim Dibble, Michael Yard, Theodore Kennedy, & many others

Studies of ecosystem drivers in rivers (especially regulated rivers) often focus on flows. Wurtsbaugh et al. 2014 Lakes Rivers

But flows may not always be the thing that limits fish populations. Wurtsbaugh et al. 2014

So what. Get your head out of the clouds Yackulic So what. Get your head out of the clouds Yackulic! Flows and fish removals are the things we can manage.

Consequences of not thinking broadly Confounding (with limited replication) Constrained decision space when considering restoration options (conflict)

Hypothesis: Phosphorous is one of the primary drivers of the Aquatic ecosystem in the regulated portions of the Colorado River Basin. Phosphorous limits primary production (i.e., plants) in many other ecosystems. In the CR Basin, most P is bound to fine clay sediments and retained in reservoirs.

Below Lake Powell, P concentrations vary by an order of magnitude, but are always low. Preliminary data. Do not cite.

Phosphorous, not flows, have been the primary driver of rainbow trout recruitment below Lake Powell since 2000 P model Flow model Preliminary data. Do not cite.

Higher phosphorous = bigger fish Preliminary data. Do not cite.

But what you all care about are the endangered fish! Grand Canyon pop (1 of 6 5) But what you all care about are the endangered fish!

~75 miles below Glen Canyon Dam, in the stronghold of Humpback chub, we still see affects of phosphorous throughout the food web

Seasonal estimates of gross primary production are highly correlated with SRP at the penstocks. Winter Spring Pre-monsoon Monsoon Preliminary data. Do not cite.

And gross primary production is linked to bugs. Preliminary data. Do not cite.

Over the last few years, declining phosphorous, gross primary production, and ultimately bugs (food) have driven fish responses Preliminary data. Do not cite.

Native fish, including humpback chub, have gotten skinnier, had lowered survival and growth, and spawned less frequently. Preliminary data. Do not cite.

At the same time, rainbow trout populations crashed system-wide. Preliminary data. Do not cite.

Bringing it back to management Important context – flows, removals, etc. Likely drivers of phosphorous export from reservoirs: reservoir fullness (policy / climate change) inflow strength withdrawal depth (policy / climate change / infrastructure) A lot of these factors also affect water temperature – another key ecosystem driver.

Summer water temperatures (F) This is what I would expect with plenty of food and without warm-water non-native species. But things could go really bad if food doesn’t keep up and/or if warm-water non-native species invade >55 55-65 65+ Summer water temperatures (F)

90 75 60 45 32 Water temperatures driven by release temperatures, discharge volume, tributary inputs, and air temperatures. Some of these can be managed. Scope for temperature management is greater in lower parts of basin. Preliminary data. Do not cite.

If the withdrawal point is constant, lowering storage can lead to rapid warming of releases. Spillways – 3648’ (Warm) Powerplant – 3470’ (Cold/Warm) River Outlets – 3374’ (Cold)

With current withdrawal point in Glen Canyon Dam, there is a tipping point around an elevation of ~3600, below which warming is rapid. Preliminary data. Do not cite.

Climate change will warm water throughout the Basin, but in lower Basin, depth of water releases is even more important. 90 75 60 45 Preliminary data. Do not cite.

Take homes Decisions that affect the quality of the water released from reservoirs will drive the future of aquatic ecosystems in the lower half of the Colorado River Basin. Flows can exacerbate or mitigate impacts of water quality.